Two-terminal electronic devices and their methods of fabrication

ABSTRACT

Two-terminal electronic devices, such as photodetectors, photovoltaic devices and electroluminescent devices, are provided. The devices include a first electrode residing on a substrate, wherein the first electrode comprises a layer of metal; an I-layer comprising an inorganic insulating or broad band semiconducting material residing on top of the first electrode, and aligned with the first electrode, wherein the inorganic insulating or broad band semiconducting material is a compound of the metal of the first electrode; a semiconductor layer, preferably comprising a p-type semiconductor, residing over the I-layer; and a second electrode residing over the semiconductor layer, the electrode comprising a layer of a conductive material. The band gap of the material of the semiconductor layer, is preferably smaller than the band gap of the I-layer material. The band gap of the material of the I-layer is preferably greater than 2.5 eV.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/467,539, filed May 9, 2012, by Yu et al., which is acontinuation of U.S. patent application Ser. No. 13/015,013, filed Jan.27, 2011, now U.S. Pat. No. 8,193,594, issued Jun. 5, 2012, by Yu etal., which is a continuation of U.S. patent application Ser. No.11/801,735, filed May 9, 2007, now U.S. Pat. No. 7,898,042, issued Mar.1, 2011, by Yu et al., which claims benefit of U.S. ProvisionalApplication No. 60/857,750 filed Nov. 7, 2006, titled“Metal-insulator-metal (MIM) devices and their methods of fabrication”naming Gong et al. as inventors, which applications are hereinincorporated by reference for all purposes. U.S. patent application Ser.No. 13/467,539 is a continuation-in-part of U.S. patent application Ser.No. 11/983,205, filed Nov. 6, 2007, now U.S. Pat. No. 8,222,077, issuedJul. 17, 2012, by Gong et al., which claims benefit of U.S. ProvisionalApplication No. 60/857,750 filed Nov. 7, 2006, which applications areherein incorporated by reference for all purposes.

FIELD OF THE INVENTION

The invention relates to two-terminal electronic devices, such asphotodetectors, photovoltaic devices, electroluminescent devices andmethods of their fabrication.

BACKGROUND OF THE INVENTION

Fabrication of electronic devices often requires multiple materialdeposition steps followed by patterning of deposited layers usingphotoresist-based techniques. These techniques can be expensive andtime-consuming. In addition, deposition processes that are used incurrent fabrication methods often involve processing under vacuum, suchas physical vapor deposition (PVD) and chemical vapor deposition (CVD).PVD and CVD apparatuses are expensive and their use increases the costsof electronic device fabrication. Moreover, stress that is developedduring deposition process and/or patterning process is often significantand leads to low manufacturing yield. Examples of such conventionallymanufactured devices include photosensing elements in digital X-rayimager made from p-i-n photodiodes based on amorphous silicon (a-Si).Plasma-enhanced chemical vapor deposition (PECVD) process used fordeposition of a thick amorphous silicon layer in such device often leadsto peeling that is encountered after the pixel in the device ispatterned. Finally, patterning of a thin film stack having multiplelayers using lithographic technique often results in an “undercut”phenomenon due to different etching rates of different layers. Suchundercut makes pixel connection in the following processing steps verydifficult.

Accordingly, there is a need for electronic devices that can befabricated with minimal patterning, with low internal stress amongdifferent layers and with reduced costs. There is also an interest indeveloping imaging elements in display and thin film sensor arrays withimproved mechanical stability.

SUMMARY

Two-terminal electronic devices, such as two-terminal photodetectors,photovoltaic devices, electroluminescent devices and high density arrayscomprising two-terminal devices that can be fabricated with minimal orno photoresist-dependent patterning, are provided. The structure of thedevices and the materials used in the device layers are selected such asto allow for less expensive processing than in traditional fabricationmethods. Such structure can also significantly improve device mechanicalproperties, device storage time and stability in operation.

In a first aspect a two terminal device (e.g., a photodetector, anelectroluminescent device, or a photovoltaic device) is provided. Thedevice includes a first electrode residing on a substrate, wherein thefirst electrode comprises a layer of metal or metal alloy; an I-layercomprising an inorganic insulating or broad band semiconducting materialresiding on top of the first electrode, and aligned with the firstelectrode, wherein the inorganic insulating or broad band semiconductingmaterial is a compound of the metal or metal alloy of the firstelectrode; a semiconductor layer residing over the I-layer, and a secondelectrode residing over the semiconductor layer, the electrodecomprising a layer of a conductive material.

In a second aspect, a two terminal device is provided, wherein thedevice includes a first electrode residing on a substrate, wherein thefirst electrode comprises a layer of conductive material (e.g. a metal,metal alloy, a conductive oxide); an I-layer comprising an inorganicinsulating or broad band semiconducting material residing on top of thefirst electrode (e.g., a metal oxide, metal nitride, metal-C—H—Oself-aligned with the first electrode or shared by a plurality of firstelectrodes in an array); a semiconductor layer residing over theI-layer, wherein the semiconductor layer may include a stack (e.g., afirst semiconductor sub-layer and a second semiconductor sub-layercomprising a p-type semiconductor); and a second electrode residing overthe semiconductor layer, wherein the second electrode comprises a layerof a conductive material, and wherein at least one of the first andsecond electrodes is transparent.

The following embodiments are applicable to the devices of both thefirst and second aspect.

In some embodiments, the semiconductor layer of the two-terminal devicecomprises an organic and/or an organometallic material. In someembodiments, the semiconductor layer of the two-terminal devicecomprises an inorganic p-type semiconductor material. In someembodiments the two terminal device is a photovoltaic device and/or aphotodetector, and the semiconductor layer is capable of absorbingelectromagnetic radiation in at least one spectral wavelength bandselected from the group consisting of near-ultraviolet, visible,infrared and combinations thereof. In some embodiments the two-terminaldevice is an X-ray detector.

In some embodiments, the semiconductor layer of the two-terminal devicepreferably comprises at least two sub-layers. In one implementation thedevice is a photodetector or an electroluminescent device, whichincludes a first semiconductor sub-layer in contact with the I-layer,that is configured to generate charge upon irradiation with light, or isconfigured to generate light after being injected with a charge. Thedevice further includes a second semiconductor sub-layer in contact withthe second electrode where the second sub-layer includes a p-typesemiconductor configured to conduct holes and block electrons. Forexample, the two terminal device may be an electroluminescent device andthe first semiconductor sublayer configured to generate light undercharge injection, may include at least one emitter selected from thegroup consisting of an organic emitter, an inorganic nano-particleemitter and combinations thereof. In one embodiment of anelectroluminescent device, the first semiconductor sub-layer is a stackof sub-layers, each of which is configured to emit light at differentwavelengths corresponding to different colors.

In one embodiment, the device is a two terminal electroluminescentdevice, wherein the first semiconductor sub-layer comprises inorganicsemiconductor nanoparticles or quantum dots.

In some embodiments the two terminal device may include a stack ofphotodetecting or electroluminescent devices.

According to some embodiments, the semiconductor layer in thetwo-terminal device comprises an organic semiconductor and furthercomprises an inorganic semiconductor as a blend with the organicsemiconductor or as a separate sublayer in contact with the organicsemiconductor sublayer.

Typically the semiconductor in the semiconductor layer has a smallerband gap than the material of the I-layer. Further, the second electrodehas a work function that is at least 0.3 eV greater than the workfunction of the first electrode, referring to absolute values.

In some embodiments the first electrode of a two terminal device is ametal or metal alloy selected from the group consisting of Mg, Ca, Sr,Ba, Ti, V, Cr, Mn, Ta, Al, Ga, In, Nb, Hf, Zn, Zr, Mo, Ni, Cu, Sn, Y anda metal alloy comprising any of these metals. The I-layer in someembodiments includes one or more of a metal oxide, a metal nitride, ametal fluoride, and a metal sulfide (or other chalcogenide). In someembodiments, the I-layer includes an oxide, nitride, fluoride, orsulfide of the same metal or metals that are present in the firstelectrode.

In some embodiments, the second electrode of the two-terminal device issubstantially optically transparent. For example, the device may be atop-sensing photodetector (or a photovoltaic device) or a top-emittingelectroluminescent device. For example, the transparent second electrodemay include a material selected from the group consisting of atransparent conductive oxide (TCO), a transparent conductive organiclayer, and a transparent thin metal layer. In some embodiments, thefirst electrode of the two-terminal device is substantially opticallytransparent. For example, the device may be a bottom-sensingphotodetector (or a photovoltaic device) or a bottom-emittingelectroluminescent device. For example, the transparent bottom electrodemay include a material selected from the group consisting of a (TCO), atransparent conductive organic layer, and a transparent thin metallayer. In some embodiments, both the first and second electrodes of thetwo-terminal device are optically transparent.

In some embodiments the semiconductor layer of the two-terminal devicecomprises an organic semiconductor selected from the group consisting ofPPV, MEH-PPV, P3HT, PTB7, PCPDTBT, PDDTT, PTZBTTT-BDT PC₆₀BM, PC₇₀BM,TPD, NPB and combinations thereof, wherein PPV ispoly(p-phenylene-vinylene), MEH-PPV isPoly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], P3HT isPoly(3-hexylthiophene-2,5-diyl), PTB7 isPoly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]],PCPDTBT isPoly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)],PDDTT ispoly(5,7-bis(4-decanyl-2-thienyl)-thieno(3,4-b)diathiazolethiophene-2,5),PC₆₀BM is (6,6)-phenyl-C61-butyric acid methyl ester, PC₇₀BM is(6,6)-phenyl-C71-butyric acid methyl ester, TPD isN,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine, NPB isN,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine, andwherein PTZBTTT-BDT has the following structure:

In some embodiments the semiconductor layer of the two-terminal devicecomprises an inorganic semiconductor selected from the group consistingof MoO, NiO, SiC, CuO, PbS, CuInSe, CuInS, CuInGaSe, CdSe, PbSe, andselenium.

The two-terminal devices provided herein are characterized in someembodiments by an Ion/Ioff ratio of at least 1000, wherein Ion and Ioffare currents detected when the device is “on” and “off” respectively.

In some embodiments the two-terminal device is a UV-detector that isincorporated into a portable electronic device and is configured toprovide a UV index to a user.

In some embodiments the two-terminal device is an X-ray or high energyradiation detector, wherein the semiconductor layer comprises: (i) afirst sublayer in contact with the I-layer, the first sub-layercomprising a material selected from the group consisting of an amorphousselenium, PbO, CdI, CdTe and HgI; and (ii) a second sublayer comprisinga p-type semiconductor over the first sublayer.

In some embodiments the two-terminal device is a UV detector, whereinthe first electrode comprises a metal selected from the group consistingof Ti, Ta, Zn, In, Sn, Ga, Zr, Y and an alloy comprising any of thesemetals; the I layer comprises an oxide of the metal or of the metals ofthe alloy of the first electrode; the p-type semiconductor layercomprises a material selected from the group consisting of TPD, NPB,polymers comprising TPD, polymers comprising NPB, polyfluorene polymers(PFO), MoO, NiO, NiN and SiC; and the second electrode is transparentand comprises a TCO or a transparent conductive polymer.

In some embodiments the two-terminal device is a visible light and/or IRdetector or a photovoltaic device, wherein the first electrode comprisesa metal selected from the group consisting of Ti, Ta, Zn, In, Sn, Ga anda metal alloy comprising any of these metals, the I layer comprises anoxide of the metal or of the metals of the alloy of the first electrode;the semiconductor layer comprises two sublayers wherein the firstsublayer is in contact with the I-layer and comprises a materialselected from the group consisting of PPV, MEHPPV, P3HT, PTB7, PCPDTBT,PTZBTTT-BDT, PDDTT, PCBM, CuO, PbS, CuInSe, CuInS, CuInGaSe, selenium,nanoparticles comprising PbS, PbSe, CdSe, CdS, and a blend comprisingthem; and the second sublayer comprises a p-type semiconductorconfigured for conducting holes and blocking electrons, and the secondelectrode is transparent and comprises a TCO, a conductive organiclayer, or a thin layer of metal or alloy. In some implementations, PCBMand/or inorganic nanoparticles are blended into the p-typesemiconductor, wherein PCBM is [6,6]-Phenyl C₆₁ butyric acid methylester

In some embodiments the two-terminal device is a top-emittingelectroluminescent device having a semiconductor layer comprising afirst semiconductor sub-layer comprising quantum dots light emitter, anda second semiconductor sub-layer comprising a p-type semiconductor,wherein the first semiconductor sub-layer is in contact with an I-layer,and the second semiconductor sub-layer is in contact with the secondelectrode, wherein the second electrode is transparent.

In some embodiments the two-terminal device is a transparentelectroluminescent device having a semiconductor layer comprising afirst semiconductor sub-layer comprising a light emitter, and a secondsemiconductor sub-layer comprising a p-type semiconductor, wherein thefirst semiconductor sub-layer is in contact with an I-layer, and thesecond semiconductor sub-layer is in contact with the second electrode,wherein both the first and second electrodes are transparent.

In another aspect an array of two-terminal photosensing or lightemission devices is provided, wherein each device comprises: a firstelectrode residing on a substrate and patterned to define the size ofeach device, wherein the first electrode comprises a layer of metal ormetal alloy: an I-layer comprising an inorganic insulating or broad bandsemiconducting material residing on top of the first electrode, andaligned with the first electrode, wherein the inorganic insulating orbroad band semiconducting material is a compound of the metal or metalalloy of the first electrode; a semiconductor layer residing over theI-layer; and an optically transparent second electrode residing over thesemiconductor layer, wherein the I-layer is not shared by the individualdevices of the array, and the semiconductor layer and the secondelectrodes are shared by the individual devices of the array. In someembodiments the semiconductor layer the semiconductor layer comprises atleast two sub-layers, wherein the first semiconductor sub-layer is incontact with the I-layer, and is configured to generate charge underlight illumination, or to generate light upon being injected with acharge, and wherein the second semiconductor sub-layer is in contactwith the second electrode and comprises p-type semiconductor configuredto conduct holes and block electrons.

In another aspect, an array of two-terminal photosensing or lightemission devices is provided, wherein each device comprises: a firstelectrode residing on a substrate; an I-layer comprising an inorganicinsulating or broad band semiconducting material residing on top of thefirst electrode; a semiconductor layer residing over the I-layer; and asecond electrode residing over the semiconductor layer, wherein theI-layer, the semiconductor layer and the second electrode are shared bythe individual devices of the array, and wherein at least one of thefirst and second electrodes is transparent. In some embodiments thesemiconductor layer comprises at least two sublayers, and wherein thefirst semiconductor sublayer is in contact with the I-layer, and isconfigured to generate charge under light illumination, or to generatelight upon being injected with a charge, wherein the secondsemiconductor sublayer is in contact with the second electrode andcomprises p-type semiconductor configured to conduct holes and blockelectrons. In some embodiments the semiconductor layer comprises atleast two sublayers, and wherein the first semiconductor sublayer is incontact with the I-layer, and is configured to generate charge underlight illumination, or to generate light upon being injected with acharge, wherein the second semiconductor sublayer is in contact with thesecond electrode and comprises p-type semiconductor configured toconduct holes and block electrons.

In another aspect a method of forming a two terminal device on asubstrate is provided. The method may include in some embodiments: (a)forming a first electrode on a substrate, wherein the first electrodecomprises a layer of metal or metal alloy; (b) oxidizing the layer ofmetal to form a self-aligned layer of a metal compound on the metallayer; (c) forming a layer of semiconductor or a stack of semiconductorlayers over the layer of metal compound; and (d) forming a secondelectrode over the semiconductor layer or the stack.

In some embodiments a method of forming a two terminal device on asubstrate includes: (a) forming a first electrode on a substrate,wherein the first electrode comprises a layer of conductive material;(b) forming a sacrificial metal-containing layer (e.g., a metal saltand/or an organometallic compound) over the layer of metal; (c) treatingthe sacrificial layer to convert it to a layer comprising a metalcompound (e.g., metal oxide, metal nitride, metal-C—H—O, and the like)suitable for an I-layer; (d) forming a layer of semiconductor or a stackof semiconductor layers over the layer of metal compound; and (e)forming a second electrode over the semiconductor layer or the stack. Itis noted that the metal of the first electrode and the metal of theI-layer may be the same or different metals.

In another aspect a method of forming an array of photosensing or lightemitting devices on a substrate is provided. The method includes in someembodiments: (a) forming a patterned first electrode on a substratewhich defines individual elements of the array; (b) forming an I-layercomprising an inorganic insulating or a broad band semiconductingmaterial over the first electrode; (c) forming a semiconductor layer ora stack of semiconductor layers over the I-layer such that thesemiconductor layer or the stack is shared between the individualdevices in an array; and (d) forming a second electrode over thesemiconductor layer, wherein the second electrodes are connected betweenneighboring pixel elements, wherein at least one of the first and secondelectrodes is transparent.

The amount of patterning during fabrication can be substantially reducedby using the methods and device structures provided herein.

These and other features and advantages of the invention will bedescribed in more detail below with reference to the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A presents a cross-sectional view of an electronic device inaccordance with some embodiments of the present invention.

FIG. 1B presents a cross-sectional view of an electronic device inaccordance with some embodiments of the present invention.

FIG. 2A presents a schematic cross-sectional view of an array ofelectronic devices in accordance with an embodiment of the presentinvention.

FIG. 2B presents a schematic cross-sectional view of an array ofelectronic devices in accordance with an embodiment of the presentinvention.

FIG. 3 is a process flow diagram for a process of fabricating anelectronic device in accordance with some embodiments of the presentinvention.

FIG. 4 is a process flow diagram for a process of fabricating anelectronic device in accordance with some embodiments of the presentinvention.

FIG. 5 is an energy diagram for one of the configurations of anelectronic device in accordance with an embodiment presented herein.

FIG. 6A is an experimental plot illustrating external quantum efficiency(EQE) dependence on a wavelength for a top-sensing image array,according to an embodiment presented herein.

FIG. 6B is an experimental plot illustrating I-V characteristics uponillumination with light of different wavelengths and in the dark, for atop-sensing image array, according to an embodiment presented herein

FIG. 6C is an experimental plot illustrating I-V characteristics for atop-sensing image array and for a bottom-sensing image array.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Introduction, Terminologyand Electronic Characteristics

As indicated, currently used fabrication methods of electronic devices(e.g., of photodetectors, photovoltaic devices, and electroluminescentdevices), employ expensive and laborious processes that often involvemultiple patterning steps. In some embodiments, electronic devicestructures that can be fabricated with a reduced number of patterningsteps are provided. In some embodiments the layers of material and thecorresponding patterning are formed using self-aligning methods, inwhich an underlying layer is modified (e.g., oxidized) to form a layerthat is aligned with the underlying layer and therefore does not requireadditional patterning process. The term “oxidation”, as used herein,refers generally to an increase in the oxidation state (e.g., from 0 to+4), and is not limited to reactions with oxygen, but also includesother oxidation reactions, such as formation of nitrides, sulfides,selenides, and fluorides from metals.

Some embodiments of the invention employ liquid-phase processing atrelatively low temperature as an alternative to costly and laboriousdeposition operations and photolithographic patterning at least for someof the components in the device structure, and particularly for the topelectrode layer.

Some embodiments of the invention employ a layer of a semiconductormaterial spanning several electronic devices in an array. The use ofsuch blanket semiconductor layer allows one to reduce the number ofpatterning steps in device fabrication. Further, some embodiments of theinvention employ a top electrode layer that is unpatterned and thatspans several devices in an array.

Several types of electronic devices can be fabricated using methodsprovided herein. These include photodetectors, photovoltaic devices andelectroluminescent devices.

Photodetectors are sensors that produce an electrical output signalafter they are irradiated. Irradiation is not limited to visible part ofthe spectrum and also includes X-ray irradiation, ultraviolet (UV)irradiation, infrared (IR) irradiation. X-ray, UV, V is, and IRphotodetectors are provided herein. Photoconductors and photodiodes areexamples of photodetectors.

Photovoltaic devices produce an electrical output signal uponirradiation that can be used to power other appliances.

Electroluminescent devices emit light in response to an electricalsignal and are also referred herein to as light emitting devices (LEDs).UV, V is, and IR LEDs can be formed using provided methods.

The electronic devices provided herein in some embodiments include atleast four layers: (a) a first electrode (functioning as a cathode)residing on a substrate, wherein the first electrode comprises a layerof metal (wherein the term “metal” includes pure metals and metalalloys); (b) an I-layer comprising an inorganic insulating or broad bandsemiconducting material residing on top of the first electrode, andaligned with the first electrode, wherein the inorganic insulating orbroad band semiconducting material is a compound of the metal of thefirst electrode; (c) a semiconductor layer residing over the I-layer andcomprising an organic semiconductor, an inorganic semiconductor or anorganic/inorganic blend, wherein the semiconductor layer is preferablyp-type; and (d) a second electrode (functioning as an anode) residingover the semiconductor layer, the second electrode comprising a layer ofa conductive material.

Other layers can be optionally included into the provided film stack,e.g., to enhance light absorption in photodetectors, or to modulate theemission wavelength in LEDs. For example, the semiconductor layer mayinclude two sub-layers, a first sub-layer configured for light emissionor photodetection, and a second sublayer comprising a p-typesemiconductor material.

As used herein, the term “over” when used to describe relative positionof the layers means that one layer at least partially overlies anotherlayer, but the two layers need not necessarily be in direct contact(e.g., there may be a another layer inserted between them). In otherembodiments, the I-layer need not necessarily be self-aligned with thebottom electrode and need not be made from the same metal as the bottomelectrode. For example, the I-layer, may be a layer of metal oxide,metal nitride, metal oxynitride, metal-O—C—H and the like, wherein thelayer is continuous and may be shared by a plurality of devices (e.g.,corresponding to individual pixels) in an array. Such layers may beprepared by coating the substrate containing patterned bottom electrodeswith a precursor containing a metal (e.g., a metal salt or anorganometallic compound), followed by treatment to form the I-layermaterial, e.g., by annealing in a suitable environment.

In general the semiconductor layer can be organic (the term alsoincluding organometallic), inorganic or be in the form of anorganic/inorganic blend or stack of individual organic and inorganiclayers. The organic semiconductor may include one or more organicsemiconductor molecules in a blend or in a stack of individual layers.The inorganic semiconductor may similarly include several inorganicmolecules in a blend or in a stack of individual layers. In someembodiments the semiconductor layer includes organometallic compounds orinorganic nanoparticles.

Materials are selected for the electronic devices such as to provide thenecessary function. Generally, the materials of the first and secondelectrodes are selected such that the difference between work functionsof the two materials is greater than 0.3 eV, e.g., the anode has a workfunction that is at least 0.3 eV greater than the work function of thecathode in absolute value. For example, in photodetectors which includetitanium as a cathode (with a work function of −4.0 eV) and an indiumtin oxide (ITO) as an anode (with the work function of −4.7 eV) thedifference in the work function is 0.7 eV in absolute value. In LEDs,the materials are selected such that the work function differencebetween the anode and the cathode is preferably at least about 1 eV,e.g., between about 2-2.5 eV. For example, tantalum, tantalum-aluminum,or tantalum-zirconium alloy can be used as a cathode in an LED, while aconducting polymer having high work function such as PEDOT (workfunction in a range of about 5.1-5.3 eV) can be used as an anode. Thedescribed electronic devices are characterized by asymmetricalcurrent-voltage (1-V) curve. In other words, a substantially highercurrent is observed in a forward bias (higher potential applied toanode) than in a reverse bias in their I-V curves. It is also noted thatnot all of the materials of the electrode need to have the requireddifference in the work function, but only the materials that directlyparticipate in charge transfer are relevant for this purpose. Forexample a titanium-coated ITO electrode, where titanium is in contactwith the titanium oxide I-layer will be characterized by the workfunction of titanium rather than ITO. Therefore, for the bottom and topelectrodes, the materials that are in direct contact with the I-layerand the semiconductor layer define the work functions of electrodes. Itis also noted that the work function of certain materials, e.g., ITO canbe tuned in a relatively broad range by changing, e.g., oxygen content,thereby allowing tuning of the required work function difference betweenthe electrodes.

Further, the material for the Mayer is selected such that its band gapis at least about 2.5 eV. Examples of such materials include metaloxides, metal sulfides, metal fluorides, etc. The band gap of thesemiconductor layer overlying the I-layer is preferably smaller than theband gap of the underlying I-layer material.

In some embodiments, the second (top) electrode is substantiallyoptically transparent. Optical transparency is determined by the type ofradiation that the device is designed to sense or emit. For example, ifthe device is a UV-detector the top electrode is preferablysubstantially transparent to UV radiation. If the device is designed tosense certain visible light wavelengths, the top electrode issubstantially transparent to these wavelengths. Examples of opticallytransparent electrodes include transparent oxides, such asindium-tin-oxide (ITO), indium-zinc-oxide (IZO), and aluminum-zinc-oxide(AZO) and thin layers of conductive polymers such as PEDOT(Poly(3,4-ethylenedioxythiophene))-based, PANI (polyaniline)-based and)PPY (polypyrrole)-based polymers. In some embodiments thin layerscontaining metals are used. For example, thin Ag/AgO electrode can beused as an optically transparent anode.

In some embodiments one or more layers of the electronic device aredeposited by liquid-phase processing. “Liquid-phase processing” refersto formation of material from a liquid-containing phase material, suchas a solution, a suspension, a sol-gel, or a melt. The liquid phase maycontain either the material to be deposited or its precursor.

The deposition of material by liquid phase processing typically involvesdelivering the liquid-phase material containing the material or itsprecursor to an underlying layer or a substrate of the device structure.In some embodiments, the liquid phase material is delivered selectivelyto the final positions where it is to be located in the electronicdevices. In other embodiments, it is delivered more broadly over a widerarea of the underlying substrate and then selectively removed by apatterning process or other process. After deposition (whether selectiveor non-selective), the deposited liquid phase material may be modified(e.g., cooled, heated, reacted, etc.) to produce a conductive layer orinsulating/semiconducting layer for an electronic device.

The liquid phase material can be delivered by a variety of methods knownby those of skill in the art. These include immersion, coating, dropletbased printing (e.g., ink jet printing), gravure printing, silkscreenprinting, thermal transfer printing, offset printing etc. Coatingmethods include spin-coating, spray-coating, bar-coating, dip-coating,slot coating and the like.

As indicated, the liquid phase material may be delivered in a patternedmanner (e.g., printing a pattern), so that no additional patterning isrequired after material is deposited. Such deposition reduces thenecessity of costly and laborious photolithographic patterning.

After the liquid phase material has been delivered to the partiallyfabricated device, the material can be formed in a number of ways. Theseinclude solvent evaporation, cooling or heating of the liquid phase,chemically or electrochemically treating a precursor in the liquidphase, treating a material or its precursor in a liquid by irradiationor high temperature to cause material precipitation. Specific examplesinclude, evaporation of solvent from a printed solution of an ink,electroplating a metal, depositing a metal by electroless deposition,depositing material by cooling a melt, etc.

In some embodiments, it is preferable to use liquid-phase deposition forthe deposition of the top electrode of the electronic device (i.e., theelectrode further removed from the underlying substrate), while thebottom electrode may be formed by conventional methods. In someembodiments, liquid-phase deposition is used to deposit a semiconductorlayer over an I-layer. In each of these embodiments, certain embodimentsfabricate at least one of the liquid phase layers by a printing/coatingprocess.

Two-Terminal Electronic Device Structure

An example of a two-terminal electronic device structure, according toone embodiment of the present invention is shown in FIG. 1A. In thisembodiment, the electronic device is a four-layer device, with anI-layer and a semiconductor layer residing between two layers ofconductive materials. It is understood, that in other embodimentselectronic devices may include additional layers, or any of the threelayers may comprise two or more sub-layers forming a stack. Across-sectional view of an electronic device (e.g., a photodetector or aphotovoltaic device) is presented. Electroluminescent devices havesimilar structures and also typically include an additional layer ofelectroluminescent material disposed over the I-layer, also referred tohere as the first semiconductor sub-layer.

The device 101 resides on a substrate 103 and includes a first electrodelayer 105, an I-layer 107, a semiconductor layer 109 and a secondelectrode layer 111. Electrical contacts (not shown) connect theelectrodes 105 and 111 to external circuit, or other components above orbelow. For example, in an image array device the bottom electrode 105 isconnected to a readout circuit underneath through a via-hole in aplanarization/passivation insulator layer.

In photovoltaic applications such as in solar cell, the two terminals ofthe device are connected to a low impedance load such as a lamp. Thedevice is operating with its internal potential created by the p-i-nstructure and flows current through the external load. In aphotodetector, operation can be conducted at a nearly zero biassimilarly to a photovoltaic cell, or at a reverse bias (connecting theanode (electrode at the p-layer side) to a voltage bias with lowpotential and n-layer side (cathode) with a higher potential). Thephotocurrent can be probed with a current meter in the loop or a voltagedrop can be read on a resistive load connected in the loop. For an LED,the anode is biased with a positive voltage (higher potential to anode).When the external biasing voltage is higher than the internal potentialcreated by the P-I-N structure in the LED, a current flows through as ina non-symmetric switch diode.

The sizes of devices can vary depending on application and can rangefrom about a few microns in high pixel density image or display array toa few centimeters in photovoltaic devices. In some embodimentsmacroscopic photodetectors or light emitting diodes (between about a fewmicrons to a few centimeters) are provided as single structures or areincorporated into an array. In other embodiments, arrays of smallelectronic devices with pixel elements sizes of between about a fewmicrons to a few millimeters are provided.

Substrate

The substrate 101 is typically made of an insulating material that doesnot allow shorting of multiple electronic devices residing on suchsubstrate (e.g., as a matrix of electronic devices). In certainembodiments, the substrate may include a conductive material (e.g., ametal), but in such cases a protective insulating coating is typicallyemployed to prevent shorting between neighboring elements or circuits.Suitable substrate materials include glasses, crystalline wafers,polymeric materials (e.g., plastic sheets) and stainless steel foils.For example, polyethyleneterephthalate (PET) can be used. Substrates canbe either rigid or flexible. In certain embodiments substrates have amelting point or glass transition point (Tg) lower than about 30° C. oreven about 200° C. The use of such substrates is possible whenfabrication process with process temperature below Tg or melting pointof a substrate is adopted, as disclosed in some embodiments in thisinvention. In certain embodiments, device 101 is constructed on top ofother circuits underneath. That is, device 101 is stacked on top ofanother circuit layer on top of substrate 103.

First Electrode

The first electrode 105 is also sometimes called the “bottom” electrodeto indicate that the electrode is closest to an underlying substrate.The first electrode functions as a cathode in the provided electronicdevices. Typically, though not necessarily, it is formed directly on theunderlying substrate. In some cases, another circuit can be insertedbetween the substrate 103 and the first electrode 105. The firstelectrode may include any suitable conductive metal (wherein the term“metal” includes metal alloys).

A variety of metals can be used as first electrode layers. For example,metals such as Ti, Ta, Al, Ga, In, Nb, Hf, Sn, Zn, Zr, Cu, Sm, Cd, Mn,Fe, Cr, Ni and Y can be employed. Alloys of these metals with eachother, such as TaAl, TaZr, TiZr and TiAl, or with other metals are alsosuitable conducting materials for the first electrode. In selectedembodiments alkaline-earth metals, such as Ca, Ba, Sr and Mg can beused. Rare earth metals, such as Sm and other lanthanides are alsosuitable. In one embodiment the metal of the first electrode includesone or more of Ti, Ta, Zn, In, Sn, Ga, Hf, Zr, Cd, V, and Nb. Forexample Ti, Ta, Zn, In, Sn, and Ga are preferred in some embodiments.Because the first electrode functions as a cathode, metals with arelatively low work function are typically selected. In some embodimentsthe work function of the first electrode is less than about 4.5 eV (fora photodetector or a photovoltaic device) or less than about 3.5 eV (foran electroluminescent device).

The first electrode 105 may be a single layer of material or may beformed of several layers forming a stack. The thickness of the firstelectrode is not critical and can be from hundreds of Angstroms tohundreds of microns or thicker. In certain applications transmission toradiation wavelength is desirable for bottom electrode, for example, ina visible-infrared photodetector array with light incidence from thebottom substrate side or for a light emitting diode arrays with lightemission from bottom substrate side. In these cases, electrode 105 canbe made with a thin metal layer, or a thin metal on top of a conductingmetal oxide (such as In₂O₃, SnO₂, or In—Sn—O) layer, that is transparentto the desired radiation. In these embodiments the bottom substrate mayalso be transparent to the desired radiation.

I-Layer

The I-layer 107 in the electronic devices of this invention includes aninorganic component which preferably has a band gap of at least about2.5 eV. In many cases, the I-layer is entirely inorganic, with noorganic component. In other embodiments, an inorganic/organic blend oran organometallic compound can be used in the I-layer. The I-layermaterial is also referred to as an insulator or a broad bandsemiconductor, and includes, in some embodiments, stoichiometric andnon-stoichiometric oxides, nitrides, chalcogenides (e.g., sulfides) andhalides of metals. In some embodiments, the I-layer includes a compoundof the same metal that is used in the first electrode. For example, ifthe first electrode is made of tantalum, the I-layer may be made oftantalum oxide, tantalum nitride, tantalum sulfide, tantalum selenideand the like. Composite oxides and inorganic ceramic nanocompositescomprising single or multiple metal anions, such as Ta—Al—O, Ta—Zr—O,Sr—Ta—O, Sr—Ti—O, Zr—Ti—O, Ca—Ti—O, Mg—Ti—O, Y_(x)Ba_(y)O_(z) (e.g.,YBaO₃) and Sm_(x)Sn_(y)O_(z) (e.g., Sm₂Sn₂O₇) are also suitable. Theycan be formed by surface oxidation from corresponding metal alloys. Insome embodiments, the I-layer includes a compound of Ti, Ta, Al, Ga, In,Nb, Hf, Sn, Zn, Zr, W, Sr, Cu, Sm, Cd, Mn, Fe, Cr, Ni, Nb or Y or theircombinations Compounds of alkaline-earth metals, such as Ca, Sr, Ba, andMg are used in some embodiments.

Various techniques may be employed to prepare the I-layer 107. In someembodiments the I-layer is formed by converting a portion of anunderlying electrode layer 105 into a desired metal compound (e.g.,oxide, nitride, chalcogenide, or halide). In this case the I-layer isformed in a self-aligned manner on top of the first electrode therebyeliminating the need of additional patterning. Examples of suchconvertion processes includes anodization, surface oxidation at anelevated temperature under oxygen and/or water vapor environment, plasmatreatment in oxygen presence, surface treatment in H₂S vapor environmentand their combinations. Similar processes have been disclosed in U.S.Pat. No. 8,222,077 which is herein incorporated by reference in itsentirety. In another embodiment, a sacrificial layer of anorganometallic compound or any metal-containing precursor (e.g., metalsalt) is formed on top of the first electrode and is then converted toan I-layer, e.g. at an elevated temperature under desired environment,such as in proper N₂, Ar, O₂, or H₂O ambient. It is noteworthy that manyof the processes of I-layer formation can be carried out at temperaturebelow 300° C., and therefore an organic substrate can be used.

The thickness of an I-layer is an important parameter that may influencethe performance of the electronic device. The thicknesses may rangedepending on specific applications. For UV, visible and infraredphotodetectors and light emitters, the thickness of the I-layer istypically in the 10-10² nm range. In direct X-ray photodetectors,I-layer thicknesses of greater than 10² nm can be used.

Of course, the actual thickness depends in part on the type of materialemployed as the I-layer and, especially on its dielectric constant orcarrier density generated by mixed-valences of metals that are involvedand oxygen vacancies that exist. For some embodiments, largerphotodetectors, photovoltaic devices, and LEDs with I-layers havingthicknesses of greater than 100 nm may be desirable.

In some embodiments, particularly in those embodiments which employorganic layers as the semiconductor layer or an emission layer, theI-layer material further serves as a diffusion barrier between theelectrode and the organic layer. In these embodiments materials havinggood barrier properties, such as metal nitrides (e.g., tantalum nitrideand titanium nitride) are particularly preferred.

Semiconductor Layer

A semiconductor layer 109 resides over the I-layer 107, and in theembodiment depicted in FIG. 1A is in direct contact with the I-layer. Inother embodiment one or more additional layers of material may beinserted between the I-layer and the semiconductor layer.

The semiconductor layer 107 typically includes a semiconductor materialthat has a band gap that is smaller than the band gap of the I-layermaterial. Although not limited, p-type semiconductors are preferred indevices with hetero junction structure. The semiconductor layer, in someembodiments, comprises a p-type inorganic semiconductor. Examplesinclude Mo—O, Ni—O, V—O, Si—C, Cu—O, Zn—O—N, Cu—In—O, Cu—In—Ga—O, Pb—S,Pb—Se, Cu—In—Se, Cu—In—S, Cu—In—Ga—Se, Cu—In—Ga—S, Cd—S, Cd—Se, Cd—Te,Pb—S, Pb—Se, Pb—Te, Pb—Ta—O. The p-layer can be a single compound film,a blend film comprising multiple compounds or a stack of films with madewith different compositions.

The semiconductor layer 109 can also be an organic semiconductor or ablend/composite film comprising an organic semiconductor binder with aninorganic or an organometallic molecule(s)/nanoparticle(s). Theinorganic nanoparticles and/or molecules in the blend and/or compositecan be the same compounds listed above in single phase, or they can bepresented in multiple layers in core-shell structures. Examples oforganometallic molecules suitable for layer 109 or as a component inblend/composite for layer 109 include M-phthalocyanine,M-Naphthalonitriles, M-porphyrin in which M=Cu, Sn, Zn, Pb) and theirsoluble derivatives. Their dimers, trimers and oligomers can also beused.

Examples of specific organic semiconductors as layer 109 or as bindercomponent in blend film 109 include polyacetylene (PA) and itsderivatives, polythiophene (PT) and its derivatives, such aspoly(3-hexylthiophene) (P3HT), PTB7, PCPDTBT, PDDTT, poly(p-phenylvinylene) (PPV) and its derivatives, such aspoly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV),polypyrrole, (“PPY”), and its derivatives; poly(2,5-thienylenevinylene),(“PTV”), and its derivatives; poly(p-phenylene), (“PPP”), and itsderivatives; polyflourene, (“PFO”), and its derivatives; polycarbazoleand its derivatives; poly(1,6-heptadiyne); polyquinolene andsemiconducting polyanilines (i.e. leucoemeraldine and/or the emeraldinebase form). Other suitable semiconducting materials include anthracene,tetracene, pentacene, tris-(8-hydroxyquinoline)aluminum (Alq3), andother metal-ligand complexes and organometallic compounds. Of thesematerials, those which exhibit solubility in organic or aqueous solventsare preferred because of their processing advantages.

Examples of PPV derivatives which are soluble to common organic solventsinclude MEH-PPV (F. Wudl, P.-M. Allemand, G. Srdanov, Z. Ni and D.McBranch, in Materials for Nonlinear Optics: Chemical Perspectives,edited by S. R. Marder, J. E. Sohn and G. D. Stucky (The AmericanChemical Society, Washington D.C., 1991), p. 683.),poly(2-butyl-5-(2-ethyl-hexyl)-1,4-phenylenevinylene), (“BuEH-PPV”) (M.A. Andersson, G. Yu, A. J. Heeger, Synth. Metals 85, 1275 (1997)),poly(2,5-bis(cholestanoxy)-1,4-phenylenevinylene, (“BCHA-PPV”). Examplesof soluble PTs include poly(3-alkylthiophenes), (P3AT), wherein thealkyl side chains contain more than 4 carbons, such as from 5 to 30carbons.

The semiconductor layer 109 can also be fabricated using donor/acceptorpolyblends. These polyblends can be blends of semiconductingpolymer/polymer, or blends of semiconducting polymer with suitableorganic molecules, organometallic molecules, and/or inorganic moleculesor inorganic nanoparticles. Examples for the donor of the donor/acceptorpolyblends include but are not limited to the conjugated polymers (e.g.,PPV, PT, PTV, and poly(p-phenylene)), and their soluble derivatives.Examples for the acceptors of the donor/acceptor polyblends include butare not limited to poly(cyanaophenylenevinylene) (“CN-PPV”), fullerenemolecules such as C₆₀ and its functional derivatives, carbon nanotubes(CNT), graphenes and organic semiconductor molecules and organometallicmolecules used heretofore in the art for photoreceptors or electrontransport layers.

A variety of charge transfer compounds may be included in thesemiconductor layer 109 (either alone or in a mixture with othersemiconductor materials described above). Such charge transfer compoundsinclude but are not limited to charge transport molecules comprisingoxadiazole groups, such as2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), and chargetransport molecules comprising arylamine groups, such as4,4′-bis[N-(1-naphthyl)-7V-phenylamino]biphenyl (NPB), and4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPB). Solublederivatives and oligomers comprising such molecular unit can also beused.

In general, the semiconductor layer 109 may comprise an organicsemiconductor, an inorganic semiconductor, or a blend or composite. Insome embodiments, the semiconductor layer 109 comprises a plurality ofsub-layers, where different sub-layers may include differentsemiconductors. For example, sub-layers of organic and inorganicsemiconductors may be stacked. In some embodiments, several organicsemiconductor molecules are blended in one layer 109. In someembodiments, distinct sub-layers of different organic semiconductormolecules may be formed in a stack. In some embodiments, severalinorganic semiconductor molecules are blended in one layer 109. In someembodiments, distinct sub-layers of different inorganic semiconductormolecules may be formed in a stack.

In addition to transferring charges, such semiconductors can alsopossess electro-optic effects, opto-electric effects or both.Electro-optic (sometimes also called electroluminescent) effect refersto electrons and holes that are injected from cathode and anode meetingand recombining to emit in the semiconductor layer, in the I-layer, ornear the interface of the I- and semiconductor layer. Opto-electriceffect refers to electrons and holes being generated under radiationwith photon energy above energy gap of the I- and/or semiconductor layerthat can be collected in external circuit connecting the bottom and topelectrodes.

For photovoltaic cell, UV, visible and infrared photodetector, thethickness of the semiconductor layer can range from about 0.1 to about 1μm. For electro-optic/electroluminescent device applications, thethickness of the semiconductor layer can be in a range of about 20-200nm. The semiconductor layer can be deposited by any suitable method,including thermal deposition, sputter, eBeam, CVD, and atomic layerdeposition. Liquid-phase processing (e.g., spin coating, slot/slitcoating, screen printing) can be used as well. We note that in arrayapplications comprising a matrix of such devices, a non-patternedcontinuous film can be used for the semiconductor layer 109. In contrastto photodetectors and photovoltaic devices made with inorganiccrystalline semiconductor wafers, the thin film semiconductors disclosedin some embodiments of this invention are either purely amorphous, orpolycrystalline with crystal grain size substantially smaller than thefilm thickness. The process adopted and the materials selected in theprovided embodiments enables one to make photosensors and photovoltaiccells with sensing layer that is substantially thinner than the sensinglayers used in crystalline wafers. Accordingly, even in high pixel countarray devices the sensing layer does not need to be patterned in theprovided embodiments (although patterning can be used if desired). Thesemethods substantially save process costs and improve process yields.

Moreover, conventional photodetectors and photovoltaic cells that aremade using inorganic covalent semiconductor wafers and films haverelatively narrow sensing bandwidth that is typically smaller than 800nm. For example the sensing wavelength range in conventional photodiodesand photovoltaic cells made using single crystal silicon,polycrystalline silicon, amorphous silicon, GaAs and InGaAs are 0.2-1mm, 0.3-0.8 mm, 0.3-0.7 μm, 0.2-0.9 μm and 0.8-1.7 μm respectively. Incontrast, organic semiconductors typically possess broader absorptionband due to ˜0.2 eV energy splitting and shift related toelectron-lattice interaction. Further, solution-based processes that canbe used in the embodiments provided herein enable forming blend filmswith multiple components having different absorption and photosensingprofiles. Thus, photodetectors and photovoltaic cells in someembodiments can have broad range of photoresponse, such as greater than1 μm. In some experimentally validated examples provided hereinphotodetectors with photoresponse from 0.3 μm to 2 μm and even greaterwas demonstrated. The detection range was thus greater than 1.7 μm.

In addition to blending semiconductors with multiple components withdifferent energy gaps, photodetectors and photovoltaic cells with broadphotoresponse range can also be made by using several sublayers ofmaterials with different energy structure.

Second Electrode

In general, second electrode 111 can employ any conductive material thathas a work function that is greater than the work function of the firstelectrode material. Preferably the work function of the second electrodematerial is at least 0.3 eV greater in absolute value than the workfunction of the first electrode material.

In some embodiments the material of the second electrode 111 issubstantially optically transparent. Examples of optically transparentelectrode materials include thin films of conductive polymers andtransparent conductive metal oxides, such as indium-oxide, tin-oxide,aluminum-zinc-oxide, indium-zinc-oxide and indium-tin-oxide.

In certain embodiments, organic conductive materials, such as conductivepolymers and oligomers are found to be particularly suitable. Conductivepolythiophene derivatives, such as poly(3,4-ethylenedioxythiophene)(PEDOT), polypyrroles (PPY), polyanilines (PANI), and co-polymersthereof can be used. Conducting nanotubes, doped fullerene molecules,graphene molecules can also be used. In some embodiments blends ofneutral conjugated polyfluorenes (PFs), PPVs and polythiophenes (PTs)and charge-transporting polythiophenes (e.g., doped polythiophenes),polyanilines and polypyrroles can be used in a top electrode 111.

Organic conductive materials often include dopants that increase theirconductivity. These dopants may be organic or inorganic (e.g., such asthose described above). Preferred organic dopants include chargedpolymers, such as poly(styrenesulphonate) (PSS), which is commonly usedin PEDOT:PSS and PANI:PSS combinations. Other suitable inorganic dopantsinclude certain metal oxides (e.g., TiO₂), dimethylsulfoxide (DMSO), andcarbon black, which are commonly used in, for example, PPY:TiO₂, andPPY:Carbon black and PEDOT:DMSO combinations.

In some embodiments metal nanoparticles, such as silver and goldnanoparticles are used in the second electrode. These materials can bedeposited by a liquid-phase processing method such as inkjet printing,screen printing, or slit coating.

According to some embodiments, precursor materials used for the secondelectrode layer are soluble in a polar or a non-polar solvent. Polar ornon-polar organic solvents, such as alcohols (e.g., methanol), acetoneor hydrocarbon solvents may be used to deliver the above mentionedmaterials using liquid-phase processing. Materials that arewater-soluble or that are soluble in organic/aqueous solutions, such asaqueous alcohols are also used in some embodiments. Such liquid mediamay be used, in some embodiments, to form the first electrode and/or theI-layer when a liquid phase deposition process is employed.

The thickness of the second electrode, similarly to the thickness of thefirst electrode is not critical and can be from hundreds of Angstroms tohundreds of microns or thicker. For the applications requiringtransparent top electrode, the thickness is often in 10 nm-1000 nmrange. For the applications requiring high conductivity over largedevice size, for example in a module of photovoltaic cell array withbottom illumination, an opaque top electrode can be used with athickness in 1-100 μm range.

Electronic Devices with Additional Layers

In some embodiments the structure of the device shown in FIG. 1A ismodified and additional layers are included to tune the electronicperformance of the device and/or to include a light-emitting layer.

A structure containing 5 layers is shown in FIG. 1B. In one embodimentthe structure shown in FIG. 1B, includes the same types of layers asdescribed with reference to FIG. 1A, with the following difference. Thesemiconductor layer is split into two sub-layers: sub-layer 110 is aninorganic semiconductor layer, and sub-layer 109 is an organicsemiconductor layer.

In yet another embodiment, an electroluminescent device can have astructure as shown in FIG. 1B, wherein layer 109 is an emission layer(also referred to as the first semiconductor sub-layer), and layer 110is a p-type (hole-transport) semiconductor layer (also referred to asthe second semiconductor sub-layer). The p-type semiconductor layer 110may be organic, inorganic or a hybrid organic/inorganic material and mayinclude multiple sub-layers or be in a composite form. Examples ofsuitable emission layer materials for layer 109 include small molecules(such as tris(8-hydroxy-quinolinato)aluminium (Alq3),bis(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminium (BAlq3),9,10-di(naphth-2-yl)anthracene (AND), 1,3-bis(carbazol-9-yl)benzene(MCP), 4,4′-bis(carbazol-9-yl)biphenyl (CBP),1,4-bis((9H-carbazol-9-yl)methyl)benzene (DCB),2,2″2″″-(1,3,5-Benzinetriiyl-tris(1-phenyl-1-H-benzimidazole (TPBi),perylene, rubrene, quinacridone and their soluble derivatives),semiconductor luminescent polymers (such as PPVs, poly(para phenylenes),polyfluorenes, poly(naphthalene vinylene)s and their derivatives) andblends of polymers with small molecules. Luminescent dopants can beadded into emission layer 109 to improve emission efficiency and/or totune emission profile and color. Examples of dopant for emission layer109 include, BCM, 3-(2-benzothiazolyl)-7-(diethylamino)coumarin(Coumarin 6), 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl) (LT-E502) quinolizino[9,9a,1gh]coumarin(C545T), Tris(2-phenylpyridine)iridium(III), Ir(ppy)₃,Bis(2-phenylpyridine)(acetylacetonate)iridium(III), Ir(ppy)2(acac),bis(1-phenylisoquinoline)(acetylacetonate)iridium(III), Ir(piq)2(acac),bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(III)(IFIrPic), 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi),4-(dicyanomethylene)-2-methyl-6-julolidyl-9-enyl-4H-pyran (DCM). Layer109 can be made by thermal deposition, or by coating or printingmethods.

Emission layer 109 can also be made with inorganic semiconductornanoparticles dispersed in an organic semiconductor binder (e.g.,materials listed above) or with the inorganic nanoparticles passivatedwith a surfactant molecules/oligomers/polymers comprising ahole-transport group (such as para-methyl triphenylamine) and polarand/or anchor group (such as pentafluorophenole) that processable in asuspension and/or a solution form. Examples of such inorganicnanoparticles including CdSe, CdTe, CdS, ZnS, Cd_(1-x)Zn_(x)S, InP,Cu₂O, Cu_(1-x)Zn_(x)O, CuS, C_(1-x)Zn_(x)S and their combinations incore-shell form or in blend form.

In direct X-ray or high energy radiation detectors, a thick non-doped orlow-doped semiconductor layer (first semiconductor sub-layer 109)containing elements with large atomic weight can be inserted between theI-layer 107 and the p-type semiconductor layer 110. Examples of thematerials suitable for such thick semiconductor layer include amorphousselenium, PbO, CdI and HgI. Selenium layer may be in an amorphous form,while the PbO, CdI and HgI compound materials may be in crystallineform. Thickness of such thick semiconductor layer is often in 10-10²micron range and high thickness is needed to optimize the carriergeneration and collection efficiency. Such detectors are biased in someembodiments in 30-300 V range to achieve optimized carrier collectionefficiency and special imaging resolution. The I-layer materials, aspreviously described, such as ZnO, TiO₂, Ta₂O₅ can be used for theseapplications with thickness of ˜100 nm, while MoO, NPB and PPV can beused for the p-type semiconductor layer (second semiconductor sub-layer)for collecting holes and blocking electrons.

Arrays of Electronic Devices

In some embodiments, arrays of electronic devices are provided on asubstrate. In some embodiments individual devices in an array correspondto individual pixels, although in other embodiments groups of individualdevices in an array may correspond to a single pixel.

An embodiment illustrated in FIG. 2A illustrates a schematicpresentation of such an array 201, where a plurality of electronicdevices (e.g., photodetectors, photovoltaic devices or LEDs) is disposedon a substrate 203. In the depicted embodiment, the first electrodelayer 205 is patterned to define the individual devices. The I-layer 207is formed in a self-aligned manner with the underlying first electrodelayer 205, and therefore does not require additional patterning. Thesemiconductor layer 207 can be deposited without patterning over theplurality of devices. Organic and inorganic semiconductors, preferablyof p-type, as described above can be used for this layer. The secondelectrode layer 211 is also deposited without patterning and spans aplurality of devices.

In this embodiment the thickness of the semiconductor layer is smallerthan the space between neighboring electrodes 205. Therefore the carrierconduction along y-direction is substantially greater than in anx-direction. Typical thickness of the semiconductor layer is 30-300 nmin LED devices, 100-1000 nm in photovoltaic and photodetector arraydevices. The ratio between the thickness of semiconductor layer and thespace between neighboring bottom (first) electrodes is typically smallerthan 0.5, preferably smaller than 0.35.

For arrays with emission or light illumination through bottom electrode205, transparent and/or semitransparent conductive film is selected forelectrode 205, wherein the transparency refers to transparency to thewavelength of interest. For such bottom-sensing or bottom-emittingdevices, the top electrode 211 does not need to be transparent. On theother hand, if emission or light illumination is arranged through topelectrode 211, transparent and/or semitransparent conductive film isselected for the electrode 211, where transparency refers to thewavelength of interest. When both top and bottom electrodes aretransparent, transparent displays or image arrays can be formed.

In some embodiments the concept is extended by stacking such two devicestogether for additional integration of function. For example, bystacking a blue LED array on top of yellow LED array, one could form alight emitting array with emission covering entire visible spectrum,from 400 nm to 700 nm. By stacking an infrared sensor detector array ontop of an LED array, one could convert the incident infrared image intoa visible light image. When the electrode layer shared by the two arraysis thin enough (typically 0.001-0.1 times of the space between twoneighboring bottom electrodes 205), such stacked device arrays withmultiple functions can be made with only the bottom electrode 205 beingpatterned. Such array devices can thus be made with simple manufacturingprocess and high yield.

Thus, functional electronic devices and array devices are built withonly one patterning operation for the first electrode layer, in thedescribed embodiment. In alternative embodiments the semiconductor layerand/or the second electrode layer can be patterned.

FIG. 2B illustrates another embodiment of an array of devices on asubstrate. In this embodiment the difference from the structureillustrated by FIG. 2A is that the I-layer 207 is not patterned and isshared by several devices. Thus, in this embodiment, the only layer thatis patterned is the first electrode layer 205. The continuous I-layer asshown in FIG. 2B can be used, for example, in a device that is preparedas follows. The first electrode 203 is deposited and patterned; then asacrificial metal-containing precursor layer is deposited, e.g., by spincoating or bar coating over a plurality of first electrodes. Then, thesacrificial layer is treated to produce an I-layer 207 (e.g., to producea metal oxide, nitride, carbide, oxynitride, metal-C—H—O, etc.) thatdoes not need to be patterned. An unpatterned semiconductor layer 209 isdeposited over the unpatterned I-layer, followed by deposition of anunpatterned second electrode 211. Of course, in other embodiments, theI-layer may be patterned after deposition (if it is deposited from asacrificial layer) to be aligned with each two-terminal device.

Methods of Fabrication of the Two-Terminal Electronic Devices

As mentioned, a variety of methods can be used to form electronicdevices provided herein.

One example of a fabrication method of a two-terminal electronic devicein accordance with certain embodiments of the invention is illustratedin FIG. 3. This example refers to an electronic device that has anI-layer formed by modification of an underlying layer. For example, inthis method the top portion of the first electrode may be modified tothereby form a metal/metal oxide, metal/metal nitride, metal/metalsulfide, metal/metal selenide or a metal/metal fluoride interface. Suchsequence is superior to other methods since it minimizes the amount oflaborious patterning steps conventionally required for electronic devicefabrication. Preferably, according to the process flow diagram shown inFIG. 3, only the bottom electrode layer may need to be patterned, whilethe I-layer is formed conformally over the patterned bottom layer, andthe semiconductor layer, and the top electrode layer is deposited as ablanket layer over several electronic devices, thereby remainingunpatterned.

The electronic device disclosed in provided embodiments with apinhole-free I-layer between the bottom electrode and the semiconductorlayer also has an advantage of eliminating leaking or shorting in theelectronic device due to a robust coverage by the I-layer. This featuremakes the devices unique over conventional devices especially for arraydevices comprising a large number of sensor or display elements.

Formation of a Bottom Electrode

Referring to FIG. 3, a layer of a first conductive material (metal) isdeposited onto a substrate in the first operation 301. A variety ofdeposition methods can be used. These include PVD methods, such assputtering, evaporation (including thermal evaporation, electron beamevaporation, sputter and the like), and photo-organic deposition methods(PODM). In selected embodiments electroplating and electrolessdeposition methods can be used, where appropriate. In other embodiments,printing can be used. For example, a variety of metals, such as Ti, Ta,Al etc. can be thermally deposited; certain metals, such as Ni can beelectroplated or electrolessly deposited; while some metals, such as Nican be printed on a substrate.

If necessary, the conductive layer deposited on a substrate is patternedusing conventional patterning methods (e.g., lithography techniques),and an I-layer is formed over at least a portion of the first conductivelayer in the following operation 303, where a portion of metal isoxidized. Several oxidation methods can be used to form the I-layermaterial, such as metal oxide, metal nitride, metal sulfide,metal-selenite, metal chalcogenide or metal halide. In some embodiments,a portion of the first electrode can be modified to form an insulatorlayer by, for example, chemical (thermal), plasma or electrochemicaloxidative treatment. According to some embodiments, an upper portion ofthe first electrode metal layer can be anodized to form metal oxide.

Anodization

Anodization is a particularly suitable technique, since it conformallycovers the first electrode metal layer with a thin layer of metal oxide,typically in a self-limiting fashion.

The anodization operation is typically performed by immersing apartially fabricated device structure into an anodizing solution,wherein the conductive layer of first electrode is connected to ananodizing potential source. The anodizing solution typically includes anaqueous solution of an acid, such as phosphoric acid, boric acid, orcitric acid. It was discovered that a salt (such as a tartrate, acitrate or a phosphate) when used instead of an acid leads to improvedanodization. In some embodiments anodizing solution may also containionic surfactants. According to some examples, after an anodizingpotential has been applied for about an hour, a thin, pinhole-free layerof metal oxide is formed on the surface of the substrate.

When anodization is performed on a patterned metal layer which haselectrically isolated portions of metal, in order to form metal oxideover these electrically isolated portions, they need to be electricallyconnected. Typically a temporary removable conducting material such assilver paste is applied to the patterned metal layer of the firstelectrode before anodization is performed, and is removed afteranodization is complete by washing the silver with a solvent, such aspropyl acetate. Anodization typically results in formation of metaloxide over the entire surface of the patterned metal layer, unless itwas intentionally protected. In some embodiments, intentional protectionof a portion of bottom electrode metal layer, may be used to form a via.Such a via may be used for connecting bottom electrode to a circuit.Certain polymers can be used as the protection pattern duringanodization and then be stripped off to form the via hole through theoxide layer. Such via holes may be used for contact pads or connectionto the bottom metal electrodes when needed.

Chemical Oxidation

Other methods of forming the I-layer by oxidizing the upper portion offirst electrode may be used. For example, chemical modification ormodification by a plasma treatment can be used. In some embodiments,metal oxides, sulfides, oxide-nitrides or nitrides may be formed bytreating the underlying metal layer with an appropriate chemical, e.g.O₂, H₂S, N₂O, N₂ or NH₃. In some embodiments, thermal O₂ oxidation oroxide formation by a chemical vapor treatment may be used. For example,a portion of a titanium layer can be thermally oxidized in O₂ atmosphereto form dense, pinhole-free titanium oxide. In other cases H₂O vapor maybe used as an oxidant to form an oxide. Chemical treatment in some casesmay be performed by a mild solution-based process and does notnecessarily involve high-temperature treatment. For example thepartially fabricated substrate can be immersed into a solution saturatedwith H₂S or CS₂ used to form metal sulfides. In other embodiments, themetal may be treated with a solution of hydrogen peroxide to form alayer of oxide. In some embodiments, formation of metal nitrides such astantalum or titanium nitrides is preferred because these materials canfunction as diffusion barriers between the bottom metal electrode 301and the semiconductor layer 305 above. In some embodiments, oxidation ofmetal involves formation of metal halide layer from an underlying metallayer by a reaction with a halogen source. For example metal fluoridelayers can be formed by treating the metal with CF₄ or SF₆, as afluoride source.

In certain applications when transparent bottom electrode 301 isdesired, a transparent electrode (such as conductive In—O, Sn—O,In—Sn—O, Al—Zn—O) can be used. A thin metal layer (for example, Ti, Ta,Hf, Zr) is then formed on top and then can be oxidized completely toform the metal compound layer 303.

Plasma Treatment

In some cases, the chemical oxidation reaction may be plasma assisted.For example, metal oxides, can be formed by exposing metal to a plasmawith an oxygen source, e.g. O₂. In one example tantalium/aluminum alloyoxide I-layer was prepared by exposing aluminum bottom electrode layerto an O₂ plasma. Metal nitrides can be formed by exposing the metal to anitrogen source (e.g., N₂O, N₂ or NH₃) in a plasma. Metal halides can beprepared by treating the metal surface with a halide source in a plasma.

When an I-layer is formed by oxidizing a portion of an underlying layerof the device by, e.g., anodization or some types of chemical treatment,the resulting device typically has an entire bottom electrode fullyencapsulated in a chemically inert wide band semiconductor material.This is an advantageous feature of this method because suchencapsulation prevents shorting between top and bottom electrodes of thedevice structure, which might otherwise occur around the edges of thebottom electrode layer.

Annealing (Optional)

Upon formation of an I-layer in operation 303, the I-layer can beoptionally annealed before operation 305, by, for example, thermaltreatment under oxygen or nitrogen ambient. In some embodiments, metaloxides formed by anodization are annealed by exposing the partiallyfabricated device to a temperature of about 60-300° C. for about 0.25-3hours.

Deposition of a Semiconductor Layer

After the top portion of the metal electrode has been oxidized, asemiconductor layer is deposited over it in the operation 305. In someembodiments the semiconductor layer is deposited by a liquid-phasemethod such as spin-coating, slot-coating, spray-coating, screenprinting, laser transfer printing, or gravure printing. These methodsare preferred when the semiconductor layer comprises organic oligomers,polymers (for example, MEH-PPV, polyalkylthiophene), compositesemiconductors with an organic binder, and liquid precursors ofinorganic semiconductors.

The semiconductor layer can also be formed by one of vacuum depositionmethods including thermal vapor deposition, sputter, CVD, PECVD, atomiclayer deposition and the like. Organic semiconductors (single molecules,dimers and trimers with molecular weight of preferably below 5×10⁴) canbe deposited by thermal deposition. Some inorganic semiconductorcompounds can also be formed by thermal deposition in vacuum or withoxygen. Examples include Mo—O, and V—O. Inorganic semiconductorcompounds can be formed by sputtering (e.g., Cu—In—O, Cu₂O), byCVD/PECVD or by atomic layer deposition (e.g, Cu—In—Ga—Se, Cu—In—S,Cu—In—Se).

For the thick X-ray absorption layer in direct X-ray photodetectors,amorphous selenium can be deposited by thermal deposition at lowsubstrate temperature. HgI, PbO can be deposited by sputtering or by oneof coating methods using a precursor solution. Saturation condensationcan also be used when a high crystalline film is desired.

Formation of Top Electrode

After the semiconductor layer has been formed, a second electrode layeris deposited in the operation 307. In certain embodiments, theconducting material of a top electrode is deposited by a liquid-phaseprocessing method. As explained above, liquid-phase processing methodsinclude printing, coating, electroplating, electroless deposition etc.Material of top electrode can be applied from a solution, a suspension,a sol-gel, or a melt. In some embodiments the material is deposited in apatterned manner. In other embodiments, a blanket layer spanning severalelectronic devices in an array is formed.

Suitable liquid dispensing techniques include immersion, coating,droplet based printing (e.g., ink jet printing), gravure printing,silkscreen printing, thermal transfer printing, offset printing etc.Coating methods include spin-coating, spray-coating, bar-coating,dip-coating, slot coating and the like.

The material can be formed from the liquid phase by solvent evaporation,cooling or heating of the liquid phase, chemically or electrochemicallytreating a precursor in the liquid phase, treating a material or itsprecursor in a liquid by irradiation or high temperature to causematerial precipitation. Specific examples include, evaporation ofsolvent from a printed solution of an ink, electroplating a metal,depositing a metal by electroless deposition, depositing material bycooling down a melt, etc.

A variety of solvents may be used to provide a liquid phase, includingpolar solvent such as water, alcohols, chloroform, etc., and nonpolarsolvents such as toluene, xylene, etc.

Liquid-phase deposition may be performed in a patterned manner (e.g.,printing a pattern) or conductive material can be blanket deposited.

The top electrode operation 307 can also be formed by one of vacuumdeposition methods such as thermal deposition (e.g., for Al, Ag, Au, Mo,etc.), sputter (e.g., for Ni, Cr, Au, In—Sn—O, Sn—O, In—Zn—O) and thelike.

After the top electrode has been deposited, the formation of anelectronic device is complete. Depending on its characteristics, thedevice may be used for a variety of purposes, e.g., as a photodetector,a photovoltaic device, or a LED.

As it can be seen, the described fabrication method reduces the numberof steps that require photolithographic patterning and vacuum processingas well as other steps associated with high costs in electronic diodeproduction. In some embodiments, methods of this invention providebetter control over electrical characteristics of the electronic deviceand expand the range of materials that can be used for fabrication.

An alternative fabrication method is shown in the process diagram ofFIG. 4. In this embodiment, the process starts in 401 by forming a firstelectrode on a substrate, wherein the first electrode includes a layerof metal. But next, instead of direct oxidation of metal, a sacrificialorganometallic layer is deposited onto the first electrode in operation403, and is then converted to the I-layer material in operation 405. Forexample, TiS₂ I-layer can be formed by depositing a thin sacrificiallayer of Ti(OPr^(i))₄ onto the first electrode layer, followed byconverting the sacrificial layer to TiS₂ by exposing the partiallyfabricated device to H₂S or CS₂. In other embodiments, the sacrificiallayer is converted to a metal oxide or partially to an M-O—C—Hcontaining film by annealing the organometallic layer. Next, in theoperation 407 a semiconductor layer is deposited over the I-layer,followed by deposition of the second electrode layer in the operation409, as it was previously described with reference to FIG. 3. It isnoted that, in some embodiments the sacrificial layer can be anysuitable metal-containing layer, including a metal salt, or pure metal,that is converted to an I-layer material upon treatment.

Energy Structure of Two-Terminal Devices

Energy structure of provided two-terminal devices, according to some ofthe embodiments, is illustrated by an energy diagram shown in FIG. 6.The diagram refers to energy levels of a device containing a cathode, anI-layer in contact with the cathode, a first semiconductor sub-layer incontact with the I-layer, a second semiconductor sub-layer in contactwith the first semiconductor sub-layer, and an anode in contact with thesecond semiconductor sublayer. The energy level of the cathode 501(typically a bottom electrode) is higher than the energy level of theanode 509. The I-layer has a wide band gap illustrated as 503. TheI-layer is configured for transporting electrons and blocking holes. Theband gap of the first semiconductor sublayer 505, that is used forphotosensing or light emission is the smallest of the band gaps of thesemiconductors in the device. The band gap 507 of the secondsemiconductor sub-layer (a p-type semiconductor) is larger than the bandgap 505 of the first semiconductor sub-layer. The second semiconductorsub-layer is configured for transporting holes and for blockingelectrons.

When the device is a light-emitting diode, higher potential is appliedto the anode than to the cathode. Holes are injected into the secondsemiconductor sub-layer, and then to the first semiconductor sub-layer.Electrons are injected into the I-layer, and are then transferred to thefirst sub-layer. Recombination of holes and electrons occurs in thefirst sub-layer and results in light emission. The blocking capacity ofthe I-layer and of the second semiconductor sub-layer confines thecharges (holes and electrons) to the first sub-layer and leads toimproved light emission efficiency.

When the device is operated as a photovoltaic cell, no externalpotential is applied to the electrodes. When the device is operated as aphotodetector or photodiode, either no external potential is applied tothe electrodes or the potential is negative, that is higher potential isapplied to the cathode than to the anode. In this instance, absorbedlight generates electrons and holes in the first semiconductor sub-layer505. Holes that are generated in the first sublayer 505 are transportedto the second sublayer 507 and are collected at the anode 509. Electronsthat are generated in the first semiconductor sublayer 505 aretransported to the I-layer 503 and are then collected at the cathode501. The blocking capacity of the I-layer and of the secondsemiconductor layer prevent the charges (electrons and holes) frommoving in an incorrect direction, especially at low bias. The wider gapof the I-layer 503 and of the second semiconductor sub-layer 507 furtheralso reduces dark current. It is noted that photovoltaic cells mayfunction with a single semiconductor layer, while it is preferable touse a bi-layer semiconductor layer for the photodetectors since thisconfiguration is particularly efficient for reducing dark current(current observed in the absence of photosignal) and improving detectionof small photosignals.

Alternative Embodiments

While in the embodiments described above, the first electrode layerincludes a layer of metal, and the I-layer includes a layer of a metalcompound made of the same metal, in alternative embodiments otherconfigurations may be used. For example, in some embodiments, the firstelectrode is any conductive material (e.g., an ITO, InZnO, AlZnO orother conductive oxide), and the I-layer is a metal compound or anorganic/inorganic blend prepared from a sacrificial layer. In yetanother embodiment, the first electrode is a first metal, and theI-layer is a compound of a second, different metal, prepared e.g., bycomplete oxidation (e.g., formation of second metal oxide, nitride,chalcogenide, or halide) of a sacrificial metal layer, deposited on afirst metal layer.

EXAMPLES Example 1 UV Detector

In accordance with one example, a UV detector is provided which has thefollowing structure: M/MO/p-type semiconductor/TCO. In some embodimentsthe metal, M, is Ti, Ta, Zn, In, Sn, or Ga. The I-layer is a metal oxidelayer, where the oxide is formed in a self-aligned manner from the topportion of the first electrode by oxidation which can be achieved byannealing the metal in O₂ environment, by treating the metal with O₂plasma, by anodization of the metal, or by heating the metal andcontacting it with H₂O₂, or by a combination of the processes listedabove In those cases where metal oxide is formed by a dry process (e.g.,O₂ plasma, heating in O₂-contained environment) or by a wet process(e.g., by anodization, or hydrogen peroxide treatment), the surface ofthe oxide may be cleaned, e.g., with a water rinse and is then dried. Ap-type organic or inorganic layer or both in stack or in a blend form isthen deposited on the clean dry surface of metal oxide. Examples oforganic semiconductors that can be used include TPD, NPB (e.g.,deposited by thermal deposition), PFO or polymers comprising TPD or NPBgroup (e.g., deposited by spin-coating or slot coating). Examples ofinorganic p-type semiconductors that can be used include MoO, NiO, NiNand SiC which can be deposited by thermal deposition, sputter orMOCVD/PECVD. Next, a top-conducting-oxide (TCO) layer, a conductivepolymer layer or a semitransparent metal layer is deposited. The onsetof the photoresponse is determined by the absorption edge of the metaloxide and the semiconductor layer (also referred to as a hole transportlayer, HTL). For example, when TiO₂ is used in the I-layer and NPB isused in the semiconductor layer the response starts at approximately 400nm. When SnO is used for the I-layer and NPB is used in thesemiconductor layer, the onset of response starts at ˜320 nm andtherefore a solar-blind UV detection can be achieved. The onset ofphotoresponse ties with the onset of interband transition or absorptionedge. At this wavelength, the electron on top of the valence band isexcited into the bottom of conduction band in either I-layer, or thebroadband p-type semiconductor layer or both which can be extracted atthe contact electrodes above and below.

In one experimentally validated example (Sample UV-A), a glass substrate(Corning Eagle 2000) of 1″×1″ was used. 100 nm Ta metal layer wasdeposited by DC sputtering using 100 W power level at a pressure of 10mtorr in argon environment. It was patterned by photolithography and bydry etching to form an array of patterned bottom electrodes 10 mm×1.8 mmin size and separated by 0.2 mm. A protection photoresist (PR) coatingwas then formed on the contact areas of Ta electrodes and the structurewas baked at 130° C. for 10 minutes. The surface of Ta was then oxidizedby anodization to form Ta₂O₅, I-layer (similarly to the process used toform two terminal M-I-M switch devices described in Example 1 of U.S.Pat. No. 8,222,077 which is herein incorporated by reference in itsentirety. The protection PR coating was then removed with a strippersolution, and the sample was then rinsed in deionized water and wasblow-dried. The sample was then sent into a vacuum chamber, where a 200nm thick Mo—O layer was thermally deposited as the p-type semiconductorlayer, and then a transparent, conductive In—Sn—O top electrode (˜100 nmthick) was sputter deposited by a direct current (DC) source at roomtemperature and under argon pressure of ˜10 mtorr. It is noted that inthis case the tantalum oxide layer is self-aligned with the bottomelectrodes, and is therefore not shared by neighboring devices, whilethe MoO layer, and the top electrode are continuous and are shared by aplurality of devices. In this sample photocurrent was observed underlight illumination from top (through the ITO layer) for wavelengthsshorter than 400 nm with external quantum efficiency in a range of20-50% el/ph.

In another experiment (Sample UV-B), the bottom tantalum electrode wasdeposited, and the tantalum oxide I-layer was formed as described forthe Sample UV-A but the semiconductor layer was 100 nm thick PFO layerthat was spin coated at 2000 rpm, as a continuous layer spanning aplurality of devices. The PFO coating was then baked at 150° C. for 30minute to remove solvent. The sample was then coated with a PEDOT:PSSsolution with a bar-coater such that it does not contact the bottomelectrode contacts. Another baking at 150° C. for 30 minutes was carriedout to remove the solvent in PEDOT:PSS, where PEDOT:PSS served as thetop electrode. Photosensitivity in the UV region was observed to besimilar to the UV-A sample described above. Dark current below 1 nA/cm²was achieved which was hardly achievable with traditional UV detectorsthat are based on SiC or GaN crystalline wafers. The low dark currentand high photosensitivity results in low detector noise and high devicedetectivity of above 10¹² Jones.

In another experiment (Sample UV-C), the substrate was a quartz plateand the bottom electrode was In—Sn—O formed by DC sputter at 100 mWpower level at room temperature. After patterning the bottom electrodewith standard wet photolithography and with acetic acid, a Zn—O—C—Hcontaining film was formed in N₂ environment from a precursor solutioncontaining zinc acetate dihydrate monoethanolamine (0.5 M) and2-methoxyethanol. The solution was coated as a continuous layer sharedby a plurality of devices and was then baked at 150° C. for 30 minutesin air or under N₂ environment to form a continuous layer of Zn—O—C—H.Next, a MoO semiconductor layer (a continuous layer spanning a pluralityof devices) and a top ITO electrode was deposited identically todeposition of these layers in Sample UV-A. A transparent UV detector wasachieved with response in 200-400 nm range. UV detection was achievedfrom both top and bottom illumination. The detector is transparent overthe entire visible range. Such transparent UV detector can be used as aUV index meter and can be integrated into a variety of portableelectronics, such as a smart watch or a mobile phone.

Example 2 Broadband NIR/Visible Light Photodetectors and PhotovoltaicCells

When narrow energy gap semiconductor is used in the semiconductor layer,absorption is shifted to longer wavelengths. IR and/or visible lightphotodetectors can be built. These devices can also be used asphotovoltaic devices.

The bottom electrode layer is a metal layer. In some embodiments themetal is Ti, Ta, Zn, In, Sn, or Ga. The I-layer is a metal oxide layer,where the metal is the same metal as used for the first electrode. Thesemiconductor layer can be organic or inorganic p-type semiconductor, oran organic/inorganic blend, or a stack. Examples of suitable materialsinclude PPV, MEHPPV, P3HT, PCPDTBT, PDDTT, CuO, PbS, CuInSe, CuInS,CuInGaSe. Such devices can be used as single detectors but areespecially suitable for detector arrays due to simplicity of theirmanufacturing process and high process yield. In the array devices, thesensor pixel can be defined by the bottom metal pattern, the remaininglayers can be deposited in blanket form over entire detector array,while the I-layer is formed over the patterned bottom electrode layer inself-aligned manner without lithographic process. The I-layer passivatesthe bottom pixel electrodes from all directions (i.e., covers the topportion and side portions of a bottom electrode)

In one experimentally validated example, 0.5 mm thick borosilicate glass(Corning Eagle 2000) was used as the transparent substrate. 200 nm thickTa was DC sputter deposited at room temperature. The Ta layer was thenpatterned into same patterns as in the UV-A example. The tantalum oxideI-layer was then formed by anodization in the same way as described inthe UV-A example. Thickness of the I-layer was chosen in this experimentto be 20 nm. The semiconductor layer was then deposited either byspin-coating or thermal deposition for organic semiconductors or by RFsputter for the inorganic compounds either directly or by depositingcorresponding metal oxides and converting them to sulfides andselenides. Samples containing PPV, MEHPPV, P3HT, PCPDTBT, PDDTT, CuO,PbS, CuInSe, CuInS, and CuInGaSe were prepared. The top electrode wasthen deposited. In one series of devices the top electrode was AZO(aluminum-zinc-oxide) formed by thermal deposition in vacuum. In anotherseries of devices the top electrode was ITO formed by sputter depositionunder argon Ar. Post annealing was performed for devices withspin-coated organic semiconductors at 150° C. for 30 minutes and fordevices with sputtered films at 250° C. for 60 minutes. The shortwavelength cut-off of the photoresponse for obtained devices is ˜400 nmfor devices with the AZO top electrode and ˜300 nm for devices with theITO top electrodes.

In another experiment photovoltaic cells in which the bottom electrodeis a cathode and the top electrode is an anode (used without externalbias) and photodiodes were formed. Device test with light illuminationfrom top revealed diode behavior with photoresponse above semiconductorenergy gap. The onset of the photoresponse coincides with the absorptionof the semiconductor layer as listed in Table 1. With soluble fullerenemolecule PCBM (as a photosensitizer) blended into the semiconductorpolymer, internal quantum efficiency near 100% el/ph was achieved. Table1 lists materials, structures, process methods and spectral responses ofthe formed devices

TABLE 1 Photodetectors having response in the NIR and/or visible regionBottom Semiconductor Layer (thickness, Top Electrode Onset of ElectrodeI-layer process means) (process means) Photoresponse Ta Ta—O (20 nm) PPV(200 nm, spin-coating) AZO (Thermal) 500 nm Ta Ta—O (20 nm) MEHPPV (200nm, spin-coating) AZO (Thermal) 590 nm Ta Ta—O (20 nm) P3HT (200 nm,spin-coating) AZO (Thermal) 640 nm Ta Ta—O (20 nm) PTB7 (200 nm,spin-coating) AZO (Thermal) 750 nm Ta Ta—O (20 nm) PCPDTBT (200 nm,spin-coating) AZO (Thermal) 1000 nm  Ta Ta—O (20 nm) PTZBTTT-BDT (200nm, spin- AZO (Thermal) 1100 nm  coating) Ta Ta—O (20 nm) PDDTT (200 nm,spin-coating) AZO (Thermal) 1400 nm  Ta Ta—O (20 nm) CuO (200 nm,sputter) ITO (sputtered) 550 nm Ta Ta—O (20 nm) PbS (Sputter) ITO(sputtered) 700 nm Ta Ta—O (20 nm) CuInSe (Sputter + selenation) ITO(sputtered) 1200 nm  Ta Ta—O (20 nm) CuInS (Sputter + sulfination) ITO(sputtered) 900 nm Ta Ta—O (20 nm) CuInGaSe (Sputter + selenation) ITO(sputtered) 1200 nm 

In other experiments, the thickness of Ta—O layer was varied in the10-50 nm range. Similar photoresponses as with 20 nm Ta—O were observed.Lower dark current was observed in a device with thicker Ta—O. This factconfirms that one can tune the thickness of the I-layer to optimizeoverall device performance.

In another series of experiments instead of Ta—O, Ti—O was used as theI-layer in similar structures. Higher forward current was observed inTi—O— containing device with the same I-layer thickness.

Example 3 Visible/Near-Infrared (NIR) Detector Array with an UnpatternedSemiconductor Layer

In this example, the bottom electrode was made with a 100 nm thick ITOor a 100 nm thick Ag layer by DC sputtering, which was then patterned bylithography to define individual devices. Titanium oxide I-layer wasformed by DC sputtering of titanium metal layer with nominal thicknessof 10 or 50 Anstrong, and then the unpatterned Ti layer was oxidized toTiO₂ by thermal oxidation at 200° C. A blend polymer semiconductorcomprising either PTB7:PC₇₀BM or PCPDTBT:PC₇₀BM (1:2 weight ratio,purchased from 1-Materials, Dorval, Quebec, Canada) was coated from ablend solution at room temperature over the I-layer and was then driedat 150° C. for 30 minutes to remove residual solvent. Toluene andchlorobenzene were used for as solvent for this study. The thickness ofthis layer (referred to as a sensing layer or the first semiconductorsub-layer) was approximately 200 nm. It is an organic semiconductor withbulk p-n junctions in nanoscale, in which photoinduced holes transportin PCPDTBT and photoinducted electrons transport in PCBM (Gang Yu etal., SCIENCE•Vol. 270, p. 1789 (1995)). The samples were then sent intoa vacuum chamber and the pressure was reduced to 5×10⁻⁷ ton. A MoO layer(a second semiconductor sub-layer) was then thermally deposited on topof the semiconductor polymer layer (the first semiconductor sub-layer)with thicknesses of 20, 40 and 80 nm for different samples. The formedMoO layer is a p-type semiconductor and is amorphous. It transportsholes to and blocks electrons from reaching the anode on top of thedevice. No substrate heating was performed during MoO deposition.

For a bottom sensing array, a 100 nm Ag layer was then thermallydeposited on top of the MoO as the top anode with optical reflection. Acover glass sheet was glued over the array area as the final passivationstep. Top sensing image array was also made with a transparent topelectrode. In this array, a thin Ag layer (10-15 nm) or a Ag/MoO blendcoating layer (1:1 ratio, 10-20 nm) were used as the transparent anode.A 200 nm SiOx was then thermally-deposited on top of whole active areaas a thin film passivation layer.

FIGS. 6A-6B show performance data for the top sensing image array madewith PCPDTBT:PC₇₀BM first semiconductor sub-layer as described above.FIG. 6A shows the spectral response, covering from 300 nm to over 1000nm. The external quantum efficiency (EQE) is over 30% el/ph in mostregions. FIG. 6B shows the current-voltage dependence in the dark andunder light illumination. The Iph-V curves were taken under 22 μW/cm² at530 nm and 16 μW/cm² at 950 nm. The dark current, is below 0.2 nA/cm²for bias within +/−0.3V and is below 1 nA in −1V to 0V range. Thephotocurrents are 3-4 orders of magnitude higher than the dark current.The corresponding peak photosensitivity was 0.18 A/W and the peak EQEwas >30% el/ph. Assuming the noise is limited by the dark current, thecorresponding detectivity D* is ˜10¹³ Jones. For a sensing element withthe bottom cathode made with strong reflection, and a thin filmpassivation with optimized transmission, the EQE can be further improvedto 60-80% el/ph.

Such an image array, in fact, can sense light from both bottom and top,as shown in FIG. 6C. Curve (a) illustrates data for a top-sensing imagearray. Curve (b) illustrates data for a bottom-sensing image array.

In another set of experiments instead of self-aligned Ti—O I-layer,solution processed Ti—O or Zn—O were used to form an unpatternedI-layer. The Zn-containing precursor was prepared by dissolving zincacetate dihydrate (Zn(CH₃COO)₂2H₂O, Aldrich, 99.9%, 1 g) andethanolamine (NH₂CH₂CH₂OH, Aldrich, 99.5%, 0.28 g) in 2-methoxyethanol(CH₃OCH₂CH₂OH, Aldrich, 99.8%, 10 mL) under vigorous stirring for 12 h.The Ti-contained precursor was prepared using a similar procedure, butthe zinc salt was substituted for a titanium salt. In devicefabrication, the Ti-containing or Zn-containing precursor solution wasspin-cast onto pre-cleaned ITO for a transparent image array or ontopatterned Ag layer for a top-sensing image array. The sample was thenannealed at 200° C. for 1 hour in air to convert the precursor into anunpatterned TiO or ZnO I-layer. The semiconductor layer and the topelectrode were deposited as described above for Experiment 3.

A 1×32 linear photodetector array used for this experiment. Each sensorwas connected to a test pad and was connected to a readout circuit(Texas Instrument, DDC264). We note that other than the bottom electrodepatterned to provide a size defining the photodiode array, and theI-layer formed by surface oxidation in a self-aligned manner with thebottom electrode, all of the layers above I-layer (the active polymersensing layer, the p-type MoO layer and the top electrode) were coveringthe entire array area without pixel patterning. Accordingly, a novelimage array with pixel pitch defined by bottom pixel contact pads isdisclosed. In the embodiments, where metal oxide was deposited from aprecursor solution and was unpatterned, the only patterned layer in thedevice is the bottom electrode.

Example 4 Infrared Photodetector Array with Onset Response in Short-WaveInfrared (SWIR) Range

Experiment presented in example 3 was repeated with the semiconductorpolymer layer (first semiconductor sub-layer) replaced by PDDTT (Y.-J.Xia et al, Appl. Phys. Lett. 89, 081106 (2006)). All other layers weredeposited as described in Experiment 3. Photoresponse of the formedphotodetector array was extended into SWIR range with photoresponseonset at >1.4 μm. In samples made with PDDTT having high molecularweight, the photosignal was detectable for wavelengths longer than 1.6μm.

In another experiment, the photodetector array was formed as describedin the Example 3 but the un-patterned blend semiconductor layer (firstsemiconductor sub-layer) was made with PCPDTBT as a binder with addednano particle PbSe (PbSe:NP) as a photosensitizer. Linear array wasprepared following a procedure that is similar to the one described inExample 3. Onset of photoresponse at 2200 nm was observed. Table 2 listsarrays of photodetectors (their structure and properties) prepared asdescribed in Example 3 and Example 4.

TABLE 2 Photodetector arrays prepared by the methods described inExamples 3 and 4. Bottom Semiconductor Semiconductor Top Onset ofelectrode I-layer Layer-1 Layer-2 electrode Photosensitivity ITO/Ti(5nm) TiO PTB7:PCBM MoO Ag:MoO 750 nm (sputter (anodized (spin-coating)(thermal (1:1, deposited and Ti, self- deposition) thermal patterned)aligned) deposition) Same as above TiO Same as above Same as above Sameas 750 nm (Thermal above oxidation, 250° C.) Ag (100 nm) TiO Same asabove Same as above Same as 750 nm (precursor above coating + annealing)ITO Same as PCPDTBT:PCBM Same as above Same as 950 nm above(spin-coating) above ITO ZnO same as above Same as above same as 950 nm(precursor above coating + annealing) ITO TiO Same as above Same asabove same as 950 nm (precursor above coating + annealing) Same as aboveSame as Same Same as above IZO 950 nm above (sputter) Same as above Sameas PCPDTBT:PbSe- Same as above Ag:MoO 2200 nm  above NP (spin-coating)(Thermal deposition) Same as above Same as Same NPB Ag:MoO 950 nm above(Thermal (Thermal deposition) deposition) Same as above Same asPDDTT:PCBM Same as above AZO 1400 nm  above (sputter or thermal) Same asabove Same as CuInSe MoO Ag:MoO 1200 nm  above (sputter (Thermal(Thermal deposition + deposition) deposition) selenation)

Example 5 Two Dimensional Image Arrays

Two dimensional sensor array can be manufactured by integrating thephotodiode arrays on top of a read out integrated circuit (ROIC) made onSi wafer. It can also be built with readout circuit made with thin filmtransistor (TFT) on a glass or a plastic substrate. The channel materialof the TFT array can be low temperature polysilicon, metal-oxidesemiconductor film, II-VI compound semiconductor film such as CdSe, a-Sifilm or an organic semiconductor film.

As an example, a 220×220 image array of photosensors was prepared. Thephotodetectors had the structure shown in Table 2 for the sample, inwhich PDDTT:PCBM polymer blend was used as the semiconductor sensinglayer (first semiconductor sub-layer). An image readout circuit wasconstructed with metal-oxide TFT (MOTFT) on glass substrate. Thephotoresponse of the array was in a range of 300 to 1400 nm. The arraywas built with a pixel pitch of 50 μm and had an active area of 11 mm×11mm. Only the bottom electrodes were patterned to each pixel pitch anddefined the size of the sensing element. The aperture ratio (the area ofthe sensing element to total pixel pitch area) was ˜80%. Thesemiconductor sensing layer (first semiconductor sub-layer), the MoOhole transport layer (second semiconductor sub-layer) and the topelectrode layer were all formed continuously over entire array area. Theimage readout follows conventional line-scan operation row by row. Acommercial gate driver chip was used as the scan driver and two piecesof commercial ROIC (readout integration circuit) chips (Flir 9717) wereused as data readout chip. The digital image signals were sent to animage processor and showed over a computer monitor. High quality imageswith 50 μm special resolution, and with dynamic range over 214 wasobserved.

Image arrays were also made with the same 220×220 image readout arrayand with the sensing layer (first semiconductor sub-layer) replaced withPCPDTBT:PCBM, and with CuInSe.

Example 6 X-Ray Detector

Large size X-ray photodetector array was prepared by placing acommercially available X-ray scintillator sheet on top of thetop-sensing two dimensional visible image array. In this experiment, a4″ diagonal MOTFT pixel readout array was designed in 320×240 formatwith pixel pitch of 255 μm. CdS:I was used as the X-ray phosphor. Itsemission profile extends in 400-620 nm range, matching well with thespectral response of PTB7:PCBM and P3HT:PCBM. In this example, the topmetal layer used for MOTFT source/drain electrode (Mo/Al/Mo stack) wasused directly for the bottom electrode material. The I-layer was formedby spin-coating a Zn-containing precursor solution over the patternedpixel electrodes (cathodes). The dried zinc precursor film was convertedinto ZnO layer after annealing at 200° C. for 1 hour. The polymer blendlayer (first semiconductor sub-layer) was then coated over the ZnOI-layer and was heated to 150° C. for 1 hour to remove solvent.Inorganic hole transport layer (HTL) MoO was used as p-typesemiconductor layer (second semiconductor sub-layer) and finally,transparent AlZnO or ITO was sputter deposited over the array as the topcommon anode electrode. 200 nm thick MoO was then deposited as athin-film passivation layer over the top anode. The CdS:I X-ray phosphorsheet was then placed over the sensing array. When X-ray beam contactsthe free surface (top) of the CdS:I, visible light emission occurs withemission intensity proportional to the incident X-ray photon density.The visible image is detected by the visible image arrays locatedunderneath the X-ray phosphor. Photocurrent corresponding to emissionintensity from CdS:I sheet is read out row by row and the analog currentsignal is converted into digital signal and transferred into image framebuffer in the image processor and displayed over the computer monitor.

Direct X-ray photosensor can also be made. In this case, the photosensorlayer (first semiconductor sub-layer) is replaced with either 300 μmthick amorphous selenium formed by thermal deposition, or a 300 μm thickPS:HgI (1:9 weight ratio) blend layer. By applying reverse bias of60-300V, sufficient photocurrent is created due to electron excitationfrom core energy levels of these materials. In this case, the X-rayscintillation layer is not needed. A listing of X-ray detector arrays,prepared in accordance with Example 6 are listed in Table 3.

TABLE 3 X-ray detector arrays. Bottom Semiconductor Semiconductor TopThin film X-ray electrode I-layer Layer-I Layer-II electrode barrierPhosphor Mo/Al/Mo ZnO P3HT:PCBM MoO AlZnO or MoO CdS:I (precursor blendpolymer ITO coating + 200° C. annealing) Same same PTB7:PCBM Same SameSame Same Same Same Amorphous Same Same Same None Selenium (300 um,thermal deposition, no substrate heating)

Example 7 Light Emission Device with Bottom Cathode

This example includes a series of experiments listed below.

In experiment 1, ITO was used as the transparent bottom electrode. Athin ZnO layer was used as the I-layer and was formed over ITO bycoating a zinc oxide nanoparticle film that was baked at 90° C. for 1hour. In this case, the I-layer serves as an electron injection andtransport layer in the light emitting device. Then, an organic layerwhich functioned as carrier transporting and light emission layer wasthermally deposited in a vacuum chamber. The thin emission layer (firstsemiconductor sub-layer) contained a blend of mCP:FIrpic (93:7 weightratio) with thickness of 10-30 nm. A p-type inorganic semiconductor MoOlayer (20-80 nm) was then thermally deposited over the emission layerand served as a hole transport and electron blocking layer (secondsemiconductor sub-layer). A 100 nm thick Ag or Al metal layer wasthermally deposited over the MoO layer as the top electrode (anode). Ahigh efficiency, bottom emission, blue phosphorescent OLED was achieved.In another experiment, the inorganic p-type MoO layer was replaced withan organic NPB layer with thickness in range of 20-80 nm. Similarperformance was observed.

In another device, by replacing the transparent bottom ITO layer withpatterned zinc metal layer, zinc oxide I-layer was formed by means ofoxygen plasma reaction or direct heating in O₂ atmosphere at 200° C.over the zinc bottom electrode. A transparent top electrode (Ag:MoO with1:1 ratio, 20 nm) was used in this example and thereby a top-emissionOLED was achieved. Other deposited layers (first and secondsemiconductor sub-layers) were the same as in the bottom emission OLEDdescribed above.

In experiment 2, alumina precursor was deposited on patterned ITOsurface by spin-coating and was converted to Al₂O₃ after heating at 200°C. in air. Examples of Al-containing precursors that are suitable forsuch deposition are described in J. Mater. Chem. C, 2014, 2, 864, whichis herein incorporated by reference in its entirety This alumina layerfunctions as the I-layer. Semiconductor layer 1 which functions as lightemission layer included organic molecule Alq (20 nm) or molecular blendCBP:Irppy3 (˜20 nm). These were deposited by thermal deposition invacuum with base pressure below 3×10⁻⁷ ton. The following layers werethe same as that used in experiment 1. Both fluorescent andphosphorescent OLED devices were fabricated. When biased at forward(high potential applied to anode) direction with voltage above 2.5 V,green light emission was observed in both devices. At a given forwardcurrent, higher emission intensity was observed in device withCBP:Irppy3. In another experiment, the I-layer was replaced with a thinTa—Al or Zr—Al alloy (˜5 nm) which was deposited by co-sputter with thecorresponding metal targets, and was then thermally oxidized toTa₂O5-x-Al₂O_(3-y) or ZrO_(2-x)—Al₂O_(3-y) layer by annealing attemperature above 200° C. Green emission was observed when biasing suchdevices in forward bias over 3V.

In another experiment, the Alq emission molecule was replaced with Balq.The other layers were not changed. Blue light emission was observedunder forward bias larger than 3V.

In experiment 3, ITO was used as the bottom electrode. Zirconia was usedas the I-layer and was formed by spin-coating a zirconium-containingprecursor solution followed by heating under oxygen ambient at 250° C.The ZrO I-layer serves as electron injection/transport layer as well ashole blocking layer. PFO-based blue, green or red emission polymers werethen spin-coated from their chlorobenzene solutions. The PFO-based layerserved as the first semiconductor sublayer. MoO or NPB were used as thep-type second semiconductor sublayer. 100 nm Ag was used as the topelectrode. Bottom emission organic light emitting devices were formedwith emission color in red, green and blue colors in visible spectralrange

A top emission device was also fabricated with a ZrAl metal alloy layerused as the bottom electrode. The surface was oxidized by oxygen plasmafollowed by baking at 200° C. In this case, transparent top electrodewas made with 20 nm Ag:MoO blend layer with (1:1) weight ratio. A 80 nmMoO layer were deposited on top of second electrode as thin filmpassivation. Other layers were the same as described above.

In experiment 4, ZnO was used as the I-layer and was formed fromZn-containing precursor solution. Red, green and blue LEDs were achievedwith CdSe quantum dots (QD) layer as the first semiconductor sublayer.It was formed by slot-coating or dip-coating of the QD solution,followed by a soft baking at 120° C. to remove solvents. MoO or NPB wasused as the second semiconductor sublayer and served as hole transportand electron blocker. It was observed that the ZnO I-layer providedsufficient electron injection, and light emission occurs at forwardvoltage right above the corresponding optical photon energies.

In experiment 5, the bottom electrode and the I-layer were replaced withTi/TiO or Ta/TaO formed with surface oxidation and used as the firstelectrode/I-layer. The two semiconductor layers were kept withoutchange. 20 nm Ag:MoO (1:1 weight ratio) was used as a transparent topelectrode. Top emission LEDs were achieved with similar operationvoltage and emission efficiency.

It is important to note that in the Experiments 4 and 5 bottom emissionand top emission LEDs were obtained with amorphous inorganic films andnanocrystalline quantum dot emitters in the semiconductor layer, Noorganic materials were present in the completely processed devices ofexperiments 4 and 5. It is also noted that if a transparent bottomelectrode of experiment 4 and a transparent top electrode of experiment5 are used in a single device, this device will be a fully transparentLED in the visible spectral range. Table 4 lists a variety of LEDsprepared as described in the Example 7.

TABLE 4 Light Emitting Diodes prepared in accordance with Example 7.Bottom P-type semiconductor Top Experiment ID Electrode I-layer Emissonlayer layer electrode (emission type) ITO ZnO mCP:FIrpic MoO3 or NPB Ag(100 nm) 1 (Blue color, (sputter) (precursor) (Thermal (Thermaldeposition) (Thermal bottom emission) deposition) deposition) Same asAl₂O₃ or Alq same as above Same as 2 (Green color, above Ta₂O₅—Al₂O₃ orabove bottom emission) (surface CBP:Irppy3 oxidation) (Thermaldeposition) Same as ZrO₂ BAlq (Thermal Same as above Same as 2 (Bluecolor, above (Surface deposition) above bottom emission) oxidation)ZrAl-alloy ZrO_(2−x) + PFO based Red, Same as above Ag:MoO 3 (red,green, blue (Sputter) Al₂O_(3−y) Green, blue (20 nm, colors, top(Surface polymer emitter thermal emission) oxidation) (Spin-coating)deposition ITO ZnO CdSe Quantum MoO₃ Ag(100 nm) 4 (red, green, blue Dots(Spin or (Thermal deposition) colors, bottom dip coating) emission) Taor Ti Ta2O5−x ot CdSe Quantum NPB or MoO₃ Ag:MoO 5 (red, green, blue(Sputter) TiO2−x Dots (20 nm) colors, top (Surface emission) oxidation)

Thermally deposited MoO was used as a passivation layer in allexperiments presented in Table 4, with the exception of Experiment 2(blue color, bottom emission), where epoxy on glass was used as apassivation layer over the top electrode.

The full names of chemicals corresponding to Example 7 are list below.

mCP is 1,3-Di(9H-carbazol-9-yl)benzene,9,9′-(1,3-Phenylene)bis-9H-carbazole, N,N′-Dicarbazolyl-3,5-benzeneFIrpic isBis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)Alq is Tris-(8-hydroxyquinoline)aluminumBAlq isBis(2-methyl-8-quinolinolato-N1,O8)-(1,1′-Biphenyl-4-olato)aluminumCBP is 4,4′-Bis(N-carbazolyl)-1,1′-biphenylIrppy3 is Tris[2-phenylpyridinato-C2,N]iridium(III)

It is noted that, when used in this application, the oxides, sulfidesand other chalcogenides mentioned in this application need notnecessarily be interpreted as stoichiometric. Thus, for example MoO,MoOx and MoO₃ may refer to the same compound.

High pixel density emissive displays can be made with the bottom cathodelight emitters shown in this example. It is noted that such bottomcathode light emitting devices are particularly suitable for activematrix displays with n-type metal-oxide TFT. Similarly to that in imagearray devices, only the bottom electrode needs to be patterned to pixellevel, while the other layers can be formed with coating over the entiredisplay area.

What is claimed is:
 1. A two terminal device comprising: a firstelectrode residing on a substrate, wherein the first electrode comprisesa layer of metal or metal alloy; an I-layer comprising an inorganicinsulating or broad band semiconducting material residing on top of thefirst electrode, and aligned with the first electrode, wherein theinorganic insulating or broad band semiconducting material is a compoundof the metal or metal alloy of the first electrode; a semiconductorlayer residing over the I-layer; and a second electrode residing overthe semiconductor layer, the electrode comprising a layer of aconductive material.
 2. The two terminal device of claim 1, wherein thesemiconductor layer comprises an organic and/or an organometallicmaterial.
 3. The two terminal device of claim 1, wherein thesemiconductor layer comprises a p-type inorganic material.
 4. The twoterminal device of claim 1, wherein the device is a photovoltaic and/ora photoconductor device, and wherein the semiconductor layer is capableof absorbing electromagnetic radiation in at least one spectralwavelength band selected from the group consisting of near-ultraviolet,visible, infrared and combinations thereof.
 5. The two terminal deviceof claim 1, wherein the semiconductor layer comprises at least twosublayers.
 6. The two terminal device of claim 5, wherein the device isa photodetector, or an electroluminescent device, and wherein the firstsemiconductor sublayer is in contact with the I-layer, and is configuredto generate charge upon irradiation with light, or is configured togenerate light after being injected with a charge, wherein the secondsemiconductor sublayer is in contact with the second electrode and is ap-type semiconductor configured to conduct holes and block electrons. 7.The two terminal electroluminescent device of claim 6, wherein the firstsemiconductor sublayer configured to generate light under chargeinjection, comprises at least one emitter selected from the groupconsisting of an organic emitter, an inorganic nano-particle emitter andcombinations thereof.
 8. The two terminal electroluminescent device ofclaim 6, wherein the first semiconductor sublayer is a stack ofsublayers, each of which is configured to emit at different wavelengthscorresponding to different colors.
 9. The two terminalelectroluminescent device of claim 6, wherein the first semiconductorsublayer comprises inorganic semiconductor nanoparticles or quantumdots.
 10. The two terminal device of claim 4, wherein the two terminaldevice comprises a stack of photodetecting or electroluminescentdevices.
 11. The two terminal device of claim 1, wherein thesemiconductor layer comprises organic semiconductor and furthercomprises an inorganic semiconductor as a blend with the organicsemiconductor or as a separate sublayer in contact with the organicsemiconductor sublayer.
 12. The two terminal device of claim 1, whereinthe semiconductor has a smaller band gap than the material of theI-layer.
 13. The two terminal device of claim 1, wherein the secondelectrode has a work function that is at least 0.3 eV greater than thework function of the first electrode, referring to absolute values. 14.The two terminal device of claim 1, wherein the metal is selected fromthe group consisting of Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Ta, Al, Ga, In,Nb, Hf, Zn, Zr, Mo, Ni, Cu, Sn, Y and a metal alloy comprising any ofthese metals.
 15. The two terminal device of claim 1, wherein the metalcompound is selected from the group consisting of a metal oxide, a metalnitride, a metal fluoride and a metal sulfide.
 16. The two terminaldevice of claim 1, wherein the second electrode is substantiallyoptically transparent
 17. The two terminal device of claim 13, whereinthe second electrode is selected from the group consisting of atransparent conductive oxide (TCO), a transparent conductive organiclayer, and a transparent thin metal layer.
 18. The two terminal deviceof claim 1, wherein the semiconductor layer comprises an organicsemiconductor selected from the group consisting of PPV. MEH-PPV, P3HT,PTB7, PCPDTBT, PDDTT, PC₆₀BM, PC₇₀BM, TPD, NPB and combinations thereof.19. The two terminal device of claim 1, wherein the semiconductor layercomprises an inorganic semiconductor selected from the group consistingof MoO, NiO, SiC, CuO, PbS, CuInSe, CuInS, CuInGaSe, CdSe, PbSe, andselenium.
 20. The two-terminal device of claim 1, wherein the device hasan Ion/Ioff ratio of at least
 1000. 21. An array of two-terminalphotosensing or light emission devices, wherein each device comprises: Afirst electrode residing on a substrate and patterned to define the sizeof each device, wherein the first electrode comprises a layer of metalor metal alloy; an I-layer comprising an inorganic insulating or broadband semiconducting material residing on top of the first electrode, andaligned with the first electrode, wherein the inorganic insulating orbroad band semiconducting material is a compound of the metal or metalalloy of the first electrode; a semiconductor layer residing over theI-layer; and an optically transparent second electrode residing over thesemiconductor layer, wherein the I-layer is not shared by the individualdevices of the array, and the semiconductor layer and the secondelectrodes are shared by the individual devices of the array.
 22. Thearray of two-terminal photosensing or light emission devices, of claim21, wherein the semiconductor layer comprises at least two sublayers,and wherein the first semiconductor sublayer is in contact with theI-layer, and is configured to generate charge under light illumination,or to generate light upon being injected with a charge, wherein thesecond semiconductor sublayer is in contact with the second electrodeand comprises p-type semiconductor configured to conduct holes and blockelectrons.
 23. An array of two-terminal photosensing or light emissiondevices, wherein each device comprises: a first electrode residing on asubstrate; an I-layer comprising an inorganic insulating or broad bandsemiconducting material residing on top of the first electrode; asemiconductor layer residing over the I-layer; and a second electroderesiding over the semiconductor layer, wherein the I-layer, thesemiconductor layer and the second electrode are shared by theindividual devices of the array, and wherein at least one of the firstand second electrodes is transparent.
 24. The array of two-terminalphotosensing or light emission devices, of claim 23, wherein thesemiconductor layer comprises at least two sublayers, and wherein thefirst semiconductor sublayer is in contact with the I-layer, and isconfigured to generate charge under light illumination, or to generatelight upon being injected with a charge, wherein the secondsemiconductor sublayer is in contact with the second electrode andcomprises p-type semiconductor configured to conduct holes and blockelectrons.
 25. A method of forming a two terminal device on a substrate,the method comprising: (a) forming a first electrode on a substrate,wherein the first electrode comprises a layer of metal or metal alloy;(b) oxidizing the layer of metal to form a self-aligned layer of a metalcompound on the metal layer; (c) forming a layer of semiconductor or astack of semiconductor layers over the layer of metal compound; and (d)forming a second electrode over the semiconductor layer or the stack.26. A method of forming a two terminal device on a substrate, the methodcomprising: (a) forming a first electrode on a substrate, wherein thefirst electrode comprises a layer of metal or metal alloy; (b) forming asacrificial organometallic layer over the layer of metal; (c) treatingthe sacrificial organometallic layer to convert it to a layer comprisinga metal compound; (d) forming a layer of semiconductor or a stack ofsemiconductor layers over the layer of metal compound; and (e) forming asecond electrode over the semiconductor layer or the stack.
 27. A methodof forming an array of photosensing or light emitting devices on asubstrate, the method comprising: (a) forming a patterned firstelectrode on a substrate which defines individual elements of the array;(b) forming an I-layer comprising an inorganic insulating or a broadband semiconducting material over the first electrode; (c) forming asemiconductor layer or a stack of semiconductor layers over the I-layersuch that the semiconductor layer or the stack is shared between theindividual devices in an array; and (d) forming a second electrode overthe semiconductor layer, wherein the second electrodes are connectedbetween neighboring pixel elements, wherein at least one of the firstand second electrodes is transparent.
 28. A two-terminal photosensing orradiation sensing device comprising: (a) a first electrode comprising aconductive material; (b) an I-layer comprising an inorganic insulatingor a broad band semiconducting material over the first electrode; (c) asemiconductor layer or a stack of semiconductor layers over the I-layer;and (d) a second electrode over the semiconductor layer or the stack,wherein at least one of the first and second electrodes is transparent.29. The two-terminal optoelectronic device of claim 28, wherein thedevice is a UV-detector incorporated into a portable electronic deviceand configured to provide a UV index.
 30. The two-terminal device ofclaim 28, wherein the device is an X-ray or high energy radiationdetector, wherein the semiconductor layer comprises: (i) a firstsublayer in contact with the I-layer comprising a material selected fromthe group consisting of an amorphous selenium, PbO, CdI, CdTe and HgI;and (ii) a second sublayer comprising a p-type semiconductor over thefirst sublayer.
 31. The two-terminal device of claim 28, wherein thedevice is a UV detector, and wherein the first electrode comprises ametal selected from the group consisting of Ti, Ta, Zn, In, Sn, Ga, Zr,Y and an alloy comprising any of these metals; the I layer comprises anoxide of the metal or of the metals of the alloy of the first electrode;the p-type semiconductor layer comprises a material selected from thegroup consisting of TPD, NPB, polymers comprising TPD, polymerscomprising NPB. PFO, MoO, NiO, NiN and SiC; the second electrode istransparent and comprises a TCO or a transparent conductive polymer. 32.The two-terminal device of claim 28, wherein the device is a visiblelight and/or IR detector or a photovoltaic device, wherein the firstelectrode comprises a metal selected from the group consisting of Ti,Ta, Zn, In, Sn, Ga and a metal alloy comprising any of these metals; theI layer comprises an oxide of the metal or of the metals of the alloy ofthe first electrode; the semiconductor layer comprising two sublayerswherein the first sublayer is in contact with the I-layer and comprisesa material selected from the group consisting of PPV, MEHPPV, P3HT,PTB7. PCPDTBT, PTZBTTT-BDT, PDDTT, PCBM, CuO, PbS, CuInSe, CuInS,CuInGaSe, selenium, nanoparticles comprising PbS, PbSe, CdSe, CdS, and ablend comprising them; and the second sublayer comprises a p-typesemiconductor conducting holes and blocking electrons, and the secondelectrode is transparent and comprises a material selected from thegroup consisting of TCO, organic conductor, thin layer of metal, andthin layer of metal alloy.
 33. The two-terminal device of claim 32,wherein PCBM and/or inorganic nanoparticles are blended into the p-typesemiconductor.
 34. The two-terminal device of claim 28, wherein thedevice is a top-emitting electroluminescent device having asemiconductor layer comprising a first semiconductor sub-layercomprising quantum dots, and a second semiconductor sub-layer comprisingp-type semiconductor, wherein the first semiconductor sub-layer is incontact with an I-layer, and the second semiconductor sub-layer is incontact with the second electrode, wherein the second electrode istransparent.
 35. The two-terminal device of claim 28, wherein the deviceis a transparent electroluminescent device having a semiconductor layercomprising a first semiconductor sub-layer comprising a light emitter,and a second semiconductor sub-layer comprising a p-type semiconductor,wherein the first semiconductor sub-layer is in contact with an I-layer,and the second semiconductor sub-layer is in contact with the secondelectrode, wherein both the first and second electrodes are transparent.